Balanced over the Unbalanced

Though most of the bidding sins thus far described could have been committed by experienced players as easily as the inexperienced, there are a few predilections that are characteristic of the latter, and one is a preference for a good, long trump suit he can see is dominant, rather than some namby-pamby 4-4 suit with no visible dominance in either hand, which is a rather curious notion if you look twice:

Q 9 5
A K 8 7
9 8 6 4
K 5
A K J 8 4
Q J 6 5
5
Q 4 3
If you are forced to ruff the second round of diamonds, you will be left with four trump in one hand, three in the other in either the 5-3 spades or the 4-4 hearts. Further, a second force on the original 5-3 fit would leave you with only 3 trump in each hand, whereas in the 4-4 fit, the second ruff would come from the now short holding, leaving you four trump intact in one hand.
Four spades looks as if it should be a cakewalk with an overtrick, and indeed, it will be with the odds-on 3-2 split. But favored splits don't always happen, in the very nature of things, and with a 4-1 split in spades, South is going to be in trouble when he knocks out the ace of clubs, whether he does this before or after all trump are drawn. Though there will be situations where he will still make game, there will be others where he is held to 9 tricks when he thought he'd make easily.
With hearts, however, you can accept a second round force in diamonds and a 4-1 trump break. You would use the Q J of hearts, after one ruff to discover the bad break, knock out the ace of clubs, ruff the diamond continuation, if forthcoming, get to dummy with the queen of spades and finish drawing trump. Indeed, you don't even need to knock out the ace of clubs for 10 tricks in hearts, though you do in spades!
If the reader is puzzled as to why this should be so, we come to one of the basic reasons for preferring a balanced suit over an unbalanced for trump: Only a trump suit allows winners beyond the number in the long hand, and you can develop this potential far more easily on a balanced suit than on an unbalanced. Indeed, you are often forced to develop this potential beyond the number in the longest holding. On the above hand, when declarer ruffs the second round of diamonds in 4 hearts, that's a heart winner and he still has four to go for five in all, with an expectation of 5 spade winners for his contract without a club winner, which will be gravy if he can get it.
But if he ruffs the second round in a spade contract, that's only one of the expected five spade winners, which with 4 heart winners makes him dependent on a club winner for ten.
(Now there is a way to increase trump winners beyond 5 on a 5-3, which is to ruff three times in the long hand while you still have trump in the short hand . It's generally referred to as a dummy reversal, i.e., using dummy as the master hand, from which viewpoint you count losers. It requires a goodly supply of entries, a 3-2 trump break if you want to cash side-suit winners later, and some good trump in dummy (well, at least one good piece) This is a complication I wish I didn't have to introduce, but I couldn't leave the false impression that ruffing in the long hand is necessarily "only" a long card you're always getting. This puzzled reader is advised to skip this paragraph for the time being.. It is sufficient to recognize that on a balanced 4-4 holding, you can increase trump winners beyond 4 by the simple expedient of ruffing in one hand and then taking four rounds of trump, but on a 5-3 holding, you don't increase trump winners beyond five by ruffing in the long hand once and then drawing trump.)
Which brings me to a second reason for preferring the balanced suit as trump when you have a choice: you can often get sluffs on an unbalanced suit and subsequent ruffs. But you can't get any sluffs on a balanced suit if you make the unbalanced trump:

A 7 5
K Q 8 3
A 7 2
9 8 6
K Q J 3 2
A J 5 2
K 6 4
7
In a spade contract, you'd better stick to game, for you can bring home only 11 tricks. In hearts, however, on a 3-2 split and spades no worse than 4-1, you will sluff a diamond on the fourth round of spades and ruff the third round of diamonds for 12 tricks. The reader might want to point out that you can sluff a diamond on the fourth round of spades even on a 5-0 split. Yes, but then it would be academic, for you'd have only one trump in dummy and you're either going to lose that 5th spade or a diamond. But on the breaks postulated, the balanced suit as trump allows slam, while the unbalanced does not.
Which brings up a third reason for preferring a balanced suit as trump: you can often ruff out a late round on an unbalanced suit.

K 7 5
A 9 8 3
K 7
A 9 8 5
A Q 6 3 2
K Q 5 2
Q 4
K 7

Here, with a loser off the top, it isn't a matter of getting sluffs. But if spades break 4-1, you'll be able to ruff out the fourth round of that suit in a heart contract, though to be sure,you're going to need an even break in hearts. But the reverse is not true. You can't ruff out the 4th round of hearts on a 4-1 break in a spade contract. Actually, there is a squeeze potential for 12 tricks in that circumstance: the defender with the long hearts must have the long clubs. But aside from that squeeze, in spades you need both major suits to break 3-2, but in hearts you need only hearts to do so provided spades are not 5-0. And surely no reader needs convincing that it's better to be dependent on one favorable break than on two.
Now let me change that hand a little:

K 8 5
A 7 6 3
A 9
K 7 6 5
A Q 7 6 3
K Q 8 4
5 4
A 8

Here there are actually three reasons why the balanced suit should serve you better as trump than the unbalanced: (1) If hearts break 3-2, spades 4-1, you can ruff out the fourth round of spades, as above. (2) If both major suits break 3-2, you can sluff the low diamond from North's hand and get a subsequent ruff, for all 13 tricks. You wouldn't want to pin your hopes for grand slam on such tenuous hopes, but people have been in worse, and in any event, the matchpoint player wants to pick up whatever extra tricks he can. (3) You can even survive a 4-1 heart break if either you don't get a diamond opening lead,or the hand with four hearts has exactly three spades. After three rounds of trump, you would simply run your spades. Given a 3-2 spade break, if the opponents didn't get off to a diamond lead, it won't matter when a defender ruffs in. You will recapture the lead, sluff a diamond on a spade, then get a ruff. If they did get off to a diamond lead, you run three spades anyway. If the defender who started with 4 hearts must follow to three leads (and his partner twice), you will simply discard the diamond on the fourth spade lead and they're not getting that diamond trick.
The above hands were constructed to establish the basic point. The skeptical reader can deal out the cards and see if the balanced suit won't work better under the conditions set forth above. In Part Two, I'm going to give actual hands to illustrate how it works in practice. But let me offer a caveat here: No one is saying there will necessarily be an advantage to the naming of a balanced suit over an unbalanced. Rather, I would offer this calculus:
On weak hands, I wouldn't be guided by this principle at all. You won't have the controls to protect a loser, draw trump, establish the side suit, then have access to it to get sluffs. I would lean toward a good strong suit, whether balanced or unbalanced. I don't want to tie myself to a weak unbalanced suit and the losers that might represent when a strong balanced suit might let me establish a crossruff. On the other hand, a strong unbalanced suit may represent the only entries to that potential as trump. I realize that many people, most perhaps, think it a mortal sin to pre-empt with a four-card suit on the side particularly a major. But I have never shared that aversion. Not for weak hands. Gimme a good sound long suit, and I'll let it override a wimpy 4-card suit any day.
With game-level bids, I would say the screw turns to where it may or may not make a difference -- you may or may not have the controls to protect a loser and develop a side suit for a sluff, but IF there is an advantage to one suit or the other, it will almost certainly lie with the balanced suit as trump.
And at the slam level, the principle comes into its own. You won't necessarily find an advantage in the balanced suit even here, but in the very nature of slam bids, you're likelier to have the controls and the ability to draw trump without losing the lead along with a side suit that can be run. Then, with all the points represented, the choosing of the balanced suit as trump can be very important, indeed.