I always use a screen protector. The challenge with the N7 is both the curved screen and the SPen. The curved screen is difficult for a lot of protectors, as they can easily not stick, leaving a lifted edge. It looks bad and it collects stuff. Also, the SPen really needs a glass-hard surface to glide on.
So far, I've used and researched tempered glass and TPU. Here's what I've found.
- Tempered glass: many brands don't have adhesive under the curved portion of the screen, so they lift. The SPen loves tempered glass - works great. The deal-breaker for me is the edge lifting and the fact that, for me, they look awful. Even from 4-5 feet away I can see the tempered glass protector, and for owners like me that use minimalist cases to enjoy the beautiful design of the N5/N7, those glass protectors really look terrible. Again, just my opinion.
- TPU: there are different grades of TPU, some are softer than others. Since most are wet-apply, I really like the chance to get it perfectly lined-up and TPU is very forgiving in that bubbles and streaks typically disappear within 12 hours or so. However, unlike glass, they suck for using the SPen as their somewhat rubbery surface grabs the SPen and the marks left behind make it hard to re-write in the same area. On the plus side, properly applied, they are almost totally invisible.
At this point I am using an Illumi AquaShield TPU and it looks amazing. The sides stick 100% and there's no issue using the cases I like to use. Aesthetically, it's just perfect. The SPen is the gotcha. The Illumi is a tad harder than other TPU's so it's better for SPen writing. And it self-heals well, so any marks that the SPen leaves on it disappear within a few minutes. But the soft TPU surface is not the best for the SPen.
I've been looking at the Samsung protector, which many say is the best for the N7. It's not a thick glass plate, but it's not a softer TPU either. The $20 - $35 price tag has me pausing for the moment.