There are two schools of thought when choosing which card to discard.
1) You could discard the J in hopes of going void in Hearts faster. If you went void early on in the hand, you could potentially use your AC to greater effect.
2) You could discard the 10. This would allow you to make a potential stop in two suits, Spades and Hearts. It is unlikely that you could go void in hearts and use your A to affect the outcome of the hand. Therefore, Keeping your Ace and Protected King is of greater importance than using your trump card effectively.