FGY is not my cup of tea theme-wise. Shrek is a better theme for me, but also not over the moon with it. The layout of those machines feels claustrophobic to me. (I'm also not a big fan of Simpsons pinball party for the same reason) also i have never found a machine of either theme that had a working mini playfield.
Ghostbusters is a theme I enjoy a lot more. and the playfield is open, with a ton of things to do. There's a ton of (in my opinion) overblown rage about the inserts on ghostbusters having minor imperfections. Given any old Family Guy or Shrek is going to have a lot more imperfections from wear and tear, i don't really see the argument being made. Having played probably 50+ credits on GB, I can tell you that those who say its 'Too Hard' are trolls, or really bad at pinball. The metal outlanes were a poor design choice by stern, but that can be resolved with acrylic outlane guards that 3rd parties are producing.
I'd go GB, but I'm not you.