You've got three types of screen protectors to consider.
Wet Application: (Invisible Shield, BodyGuardz, etc.)
These are the type that require a liquid to apply, and time to set in (usually 2-3 days). They come in screen and full body coverings. There is a slight texture to them, but they are near impervious to scratches. Peeling at corners is a known issue, but otherwise, they rarely need to be replaced.
Dry Film with little to no adhesive: (Martin Fields, Seidio, Steinheil, Clarivue, etc.)
These types can be tricky to apply, but are supposedly washable and reusable (I've had poor luck with trying to reuse). They typically offer the best feel and clarity of the 3 protector types, but they scratch easily (it's basically a plastic overlay over your glass screen), meaning they need to be replaced based on your usage pattern. These are the types I use, and I typically get 9-12 months out of them.
Thin adhesive film:
This is the garbage you'd find in 10-packs for $1, or at mall kiosks. It's literally a paper thin film that is very malleable offering minimal protection. Since it's not rigid like the above type, it's harder to get rid of air bubbles. These are only useful as a temportary protector until one of the better types from above arrives.
There's always going to be a debate between the wet and dry application types. There are fan(boy)s of each types. I prefer using the dry application and a good case. Some prefer the wet application so they don't need to use a case. I see almost no point in using the wet application for screen only.
As for brand loyalty, here's where it gets worse. Within each sub category, they're all practically the same. You have to look for the minor differences. For example, Martin Fields includes a screen protector AND a camera lens protector in each pack, but they charge about 3 times what the other companies do. Also, MF and Seidio are the only ones still using the ancient peel and apply method with no tabs. SGP uses a method with 3 layers and two tabs, making installation much less frustrating. So if you go with the dry application, I recommend either SGP (Steinheil), or MF if you really want the camera lens protector. No idea on Clarivue as I haven't used them yet, but I'd avoid the Seidio.