MP pairs. You are south and you pick up:

♠ 2
♥ Q 4
♦ A Q J 7 6 5
♣ J 5 3 2

What is your bid?

A 2♣
B 3NT
C 3♦

A 2♣ (0 votes)
2♣ is pointless. Many bridge players try Stayman in the hope of finding a feeling of security: 'If partner replies 2♠, I will bid 3NT.'
'Security'? What if partner holds ♠5432?
And what if partner does not reply 2♠? Do these players than continue with 5♦? Partner, holding ♠AKQ, might lose three top tricks while 3NT turns out to be on ice...
(Another 'detail': if partner replies 2♥ he might still hold four spades...).

B 3NT (27 votes)
3NT is correct. South cannot find out which game is best but experience shows that opposite a balanced hand 3NT is usually better than five in a minor suit. Only rarely it will turn out 5♦ was better after all but by not revealing his hand, south will more often score game in 3NT thanks to an 'unlucky' lead.

C 3♦ (10 votes)
3♦ is pointless. This hand is not strong enough for a slam, so 3♦ is obviously intended to offer partner a choice of games (5♦ or 3NT). But on the basis of what considerations can partner then decide? He does not have a clue! The 3♦ bid therefore only helps the opponents.
Without advanced bidding tools you cannot find out whether this is that rare case where 5♦ is better than 3NT. Therefore you should bid the game that usually is best: 3NT. The additional advantage is that you do not reveal your hand to the opponents (that is why most top players, who do have the tools to find out, would probably still jump directly to 3NT).
(Suppose you bid 3♦ and partner ventures 3NT - as said before, he has no idea. East now has been warned about the long diamond suit in dummy. He might take a look at dummy by leading an ace and thus find the killing defence (often good tactics when the defence must cash out as quickly as possible).
A practical advise therefore: only bid 3♦ as an invitation for a slam, so the bid shows a stronger hand than this one.