Cummins is obviously younger and has more room for improvement, but I think Pattinson's a slightly better prospect at the moment.
Pattinson looks like he's going to be more durable, his action is so simple and repeatable, and he looks physically stronger and fitter. He maintains his pace well and he's just got such sound fundamentals, good pace, consistently puts the ball in decent areas and he's shown an ability to move it either way. I'm not getting carried away because this was only NZ
and both decks were pretty spicy, but with his natural attributes I can see him being succesful for a long time to come.
Cummins seems to hit the deck harder and perhaps have a bit more of an x-factor about him, but his action and physique need a lot more refinement before he's going to be consistent and durable at the highest level imo. Action is a bit twisty, pace drops away noticably later in spells and he doesn't yet possess the bowling nous and control which Pattinson has displayed. Although given his obvious talent and maturity it wouldn't suprise me if he polishes these areas up pretty quickly.