Choose by waiting to see which one you're most in the mood for on the day. Be sure to take your time playing whatever you pick as well, you'll not enjoy whatever you pick if you rush through to get to the other games/stress over the new stuff.

I push the old a-side for the new. At least have a peek at the new game(s), anyway. But if I know that two new ones will arrive on the same day I think about what sort of games they are in order to pick. Is one a game you could just dip in and out of? In this case I'd try the dipper for a short time first to satisfy curiosity.

Good luck with picking one out!