Mechanically I just want a balanced system that gets out of my way and lets the table go through an adventure and have fun. I tried running Pathfinder a few times but there's just too much for me to track with it. It sort of gets in my way. That's not fault of the system, I'm just not the audience for it.
5e is much simpler and does a pretty decent job with balance. It's not perfect, by any means, but pretty much any build is going to have its shine moments and there's only a few spells here and there you need to be aware of as a GM that can be problematic.
What it does worse than Pathfinder for me though: It's not owned by Paizo.
I really really miss the OGL, the 3rd party support from tools like Hero Lab, Realm Works, etc. I miss the world setting and fantastic module/AP support. I miss the card game tie in and PFS.
Paizo is hands above the better ran company. If they came out with a Pathfinder Basic that was basically 5.5e I'd be a very happy camper.