A Major vs. No Trump

When there seems to be a viable choice between a major suit (i.e., 8 pieces) and no trump (i.e., all suits appear to be stopped), experienced players will tend to opt for the trump contract. The theory behind that inclination is that when the suit is 4-4, you'll probably get a ruff sooner or later in some suit, that extra trick not only justifying the one-trick higher needed for game, but at the same time perhaps serving as a stopper in your weakest suit. Indeed, the Stayman Convention is specifically geared to smoking out a 4-4 major suit fit when someone has opened a no trump. And if the fit is 5-3 where you may or may not have ruffing potential in the short hand, or 6-2 where you probably won't, that dominant suit will serve as a stopper to a run on a weak suit, and if in an otherwise weak hand, might serve as your only entries to that long-card potential.
However, this preference is not near so pronounced as preferring a major over a minor, or no trump over a minor, and it's not terribly rare to find a deliberate choice of no trump even with knowledge of an 8-card fit. One might do that on a very strong but flat 4-3-3-3 hand (one of those 3's being opposite a five-card major). With assurance that every suit is adequately stopped and no hope of a ruffing potential, one might opt for no trump for the extra ten points if the number of tricks to be gained is the same in each contract. Or, conversely, with three small pieces opposite a 5-card major and solid strength in the other 3 suits, one might opt for no trump on the expectation that he might avoid that suit, unless his partner's strength is concentrated there, and perhaps run more tricks than those pairs tied to a possibly weak suit.
When the fit is more than 8 pieces, any inclination toward no trump tends to dissipate. Well, on to some hands.
10 7 6
A 9 7 2
A 10 9 6
8 7
A K J 5 8 4 2
J 4 3 K 6
8 3 Q 10 5 2
9 8 6 2 J 10 7 5
Q 9 3
Q 10 8 5
K J 7
A K Q

South opened a no trump and his partner then employed the Stayman Convention to smoke out the 4-4 heart fit. He then gave his partner a raise to three and South took it on to four. It's a tenuous contract, and it might not have mattered whether they were in 3 no or 4 hearts -- give East one of the top spade honors, same distribution, and each could be set one trick -- but the cards were such that it did matter.
West opened with the king of spades and had to shift lest he establish the queen, and now South can make his contract if he reads the cards right. He must hop up with the ace if a heart is led, take three rounds of clubs, sluffing a spade, then get to dummy with the ace of diamonds to lead a heart toward his queen. He will later use a spade ruff for an entry to take the diamond hook.

A 4
K J 3
Q 9 8 7 2
A 6 3
Q 9 8 7 6 J 3 2
Q 7 A 10 2
5 3 A J
K 9 8 2 Q J 10 7 4
K 10 5
9 8 6 4 2
K 10 6 4
5

Despite South's rather meagre heart suit and the certain stopper in clubs, this hand will fare significantly better in hearts. It's awfully risky to play unbalanced hands in no trump with a single stopper in a suit, unless you have some expectation of running your nine tricks off the top. But four hearts wouldn't be a bad contract here, though it will require some care in the playing. You definitely don't want to use a club ruff to get to the South hand in order to take the heart finesse.
You might note also that the hand illustrates the major-over-minor principle. Despite the considerably stronger diamonds, the hand won't make game in that suit. You're going to have to lose two hearts and the ace of diamonds whichever suit is trump..

10 5
K Q J 8 7 5
Q 9 5
6 5
A J 2
9 6
K 10 8 5
A K J 5

The 6-2 fit illustrates both the entries a long suit establishes for itself as trump and the protection it offers against the run of the opponents' dominant suit. In no trump, you would have a double stopper in every suit, and certainly the potential for nine winners. But unless West holds the diamond ace or the stiff ace of hearts, the defense will be able to deny you access to the heart suit beyond the first winner (or 2nd winner if East has a stiff ace), and you'll be fighting for your tricks out of the closed hand.
Four hearts wouldn't be a certainty by any means, for you're going to have to avoid a second diamond loser, but you have several chances for doing so and you're at least in the ballpark on a game bid there.

However, as mentioned earlier, the preference is not so pronounced as that over a minor:

J 10 5
10 3 2
K Q 10 9 7
K J
A Q 7 9 8 6 3 2
9 6 5 A 8
8 4 J 6 5
A 10 8 6 5 9 4 2
K 4
K Q J 7 4
A 3 2
Q 7 3

This hand came up in a Vanderbilt Knockout, one pair playing it in three no without even mentioning hearts, the other pair in four hearts. You can see that, as the cards lie, three no will make while four hearts will not. However, that doesn't prove too much. For it takes a bit of bad luck (the spade hook being off) to doom four hearts, and considerably more good luck (the spade suit being blocked and unbalanced) to make three no possible. Indeed, I would hazard the guess that if you shuffled and dealt out the E-W cards 20 or 30 times, four hearts would prove makable considerably more often than three no. But who can tell how the cards will lie during the bidding?

One last hand. This will produce an overtrick in either 3 no or four hearts, so both contracts are safe. But to the matchpoint player, that extra trick furnished by a ruff -- and thus extra 20 points on the score -- becomes important.

J 6 5
Q 7 6 2
A J
Q 9 6 3
K Q 9 7 10 4
8 4 3 K 5
Q 9 7 6 5 4 3 2
K 8 J 7 5 4 2
A 8 3 2
A J 10 9
K 10 8
A 10

West can't attack spades profitably, so declarer can take the diamond hook with impunity. Even if it loses, he'll still get the full value of his ace and king. Since the finesse is on, the most likely way to take it, declarer always has in no trump four hearts, three diamonds, two clubs and a spade for 10. In hearts, declarer can take the same finesses, only now he can sluff a spade on the long diamond, and after three rounds of trump, he will cash the ace of clubs, then establish the queen. Subsequently, after cashing the ace of spades, and losing a spade, he will ruff a spade in dummy, cash the queen of clubs and ruff a club in the closed hand. That's not two extra tricks in the trump contract, since the fourth heart would have been a winner in no trump, but it is one extra trick, which translates into the above-mentioned 20 more points.