Both are equally winning -- I would simplify in a heartbeat to eliminate any potential issues that might arise from my own mistakes. a5 may be the object best move, but I'd have a much easier time converting the win after Qxd4. This is probably a good poor example of a very "human-like" move in a position where there is also a competing, and superior, "engine-like" move.
[J'adoube: I guess it's hardly a good differentiator if the "engine-like" move is also obvious to many humans...]
"Simplify, simplify."
My thoughts exacly. Make is so plaifully obvious to your opponent that his demise is unstopable that he feels compeled to resign. Make every shred of hope dissapear from his eyes.
Because the knight is so poorly placed, and because even if it miraculously manages to win either the pawn or the queen it's still an easy win, in this example I'd just push the pawn.
But you're right, in most cases I'd sac to simplify into a less complicated winning position.
since both moves clearly result in a win, they are equally good, objectively. QxN is the best move. (note that even if somehow you lose on time its still a draw after qxn)
That's a good point, if I had less than a minute, especially without the use of pre-move I'd just sac the queen because the knight can give at least 1 check now or later to burn additional seconds of reaction time.
If I had anything more than a minute, and I'd been playing up to this position all in one sitting, I'd surely realize the knight is so useless here that I'd have no need to sac... not that I woudn't give up my queen, for example on move 3 I'd let him have it.
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OK, so you have the following (hypothetical) situation, you are clearly winning, but your opponent is playing on, as is his constitutional right.
Do you play the best move a5, or just Qxd4, removing all hope for a swindle?
I actually found that the second choice often leads to immediate resignation, thus a quicker win.