I used a Skinomi screen protector before and was satisfied. Verizon sells a glass screen protector, but DO NOT buy it. The screen and speaker panels do not sit flush, which causes the protector to not sit right. Massive bubbles.
I picked up the Zagg Glass at my local Zagg Store. It was well worth it in my opinion. As danwanna pointed out -- it only goes over the screen and not speakers - which is fine for me. I use it with a incipio feather case.
I got the Glass-M protector from Amazon and really like it. It almost works with the Dot View case since it is so thin. I'm hoping that the hinge will stretch out a little over the next couple days and it will close the rest of the way.
The only thing I dislike about the Glass-M and I assume all of the other 15mm protectors is that it doesn't have rounded edges. It isn't a big deal since it is so thin, but I miss the smooth edges of the original glass protector.
I picked up one of the Verizon ones today because I screwed up and got some dust under the last one. OCD made me take it off. I put this one on using the hinge method in a steamy bathroom and it is perfect.