[Buty2008]

I learned this game long time ago. Basic rule second in trick play low. Rule of 11: 11-4 (value of lead card)-4 (dummy's & declarer's higher cards number)= 3 higher cards in RHO give no useful info.
I stick to 2nd play low:
If A or J comes out from RHO I have 2 tricks in suit.
If I use the Q to cover a smaller card I will play any finesse from hand to dummy to let RHO return the suit.
Worse case if LHO get to lead again low in the same suit. Then I need to guess if A or J are in LHO hand.
To play 10 is based on premise that 4 is lead from a suit with an honor (A or J):
If RHO play small I have 2 tricks in suit.
If RHO play J I win with Q, than I play small to dummy's K.
If RHO play A I have 2 tricks in suit.
It seem 10 is better but exist the case LHO has lead from 4 small cards suit. RHO with AJx, cover 10 with J, and dummy's K with ace and is able to play his 3rd card to give LHO 2 more tricks in suit. That is really bad.
Here come the need to know how high is NT contract.
In a 1NT contract declarer has no long suit to play its winners and get more clues about what values are in LHO or RHO hands & no other winners in dummy to play low toward that.
In a higher NT contract is supposed declarer & dummy have a number of straight winners that can be played to force LHO or RHO to drop a card from leading suit, making things clear.

[billw55]

I will try writing this out long form. The key is to imagine cases where it matters if I play the ten or low.

Case 1, LHO holds the A and J: I am always getting two tricks. Conclusion: no difference between low and ten.

Case 2, honors are split: I make two tricks by playing the ten. If I play low, I will have to guess correctly on the second round. RHO may occasionally play an honor on trick one in error, giving me two tricks. However this does not gain since playing the ten always makes two tricks anyway. Conclusion: the ten is better.

Case 3, RHO has both honors: If he has AJx, then I cannot make two tricks legitimately. However, if I play low from dummy he might play an honor, depending on his spot card. If I play the ten I have no chance. If he has AJ tight, low makes two tricks automatically, although this may be unlikely based on the apparent 4th best lead. Meanwhile the ten still fails, as I am never playing to drop the ace on the second round. Conclusion: low is better.

So basically I must decide if case 2 or case 3 is more likely. I think it is pretty clear that case 2 is more likely: xxxx is not an appealing suit to lead, and also some players will lead a higher spot from this holding. Not to mention that split honors is twice as likely on statistics alone. Final conclusion: the ten is better.

Of course this ignores other possible considerations. For example, the inference that xxxx is an unappealing lead is up for debate: this may not be valid if the auction warned against other suits, or if the contract is 6NT, or if the player is weak. Or the full deal may present other issues in the play. But absent any of that, the ten is clearly correct.