Here are some things you ought to think about when mask shopping:
How big is your head?
If you have a little spider monkey skull, then Dye Invisions will work nicely, as they are a little smaller than most other masks. This means that they present a touch less target, but if you are hydroencephalitic, your misshapen potato of a head will poke out all over the place and you won't enjoy as much protection.
Do you wear glasses?
If you do, you will want a mask that has more room for them, and perhaps one that supports a fan. The Profilers from Vforce have enough room for most glasses, and the foam doesn't cover where the frame leads back to your ears, which is nice. On the other hand, they don't have a fan available to use with them, like JT or Dye masks.
Does it bother you if the mask moves around a little, or does firm foam around the goggle bother you more?
Having something on your face all day is irritating anyway. You should try on masks, as others have said. When you do, press it to your face, shake you head vigorously, and when the spots clear from your vision, assess whether the mask moves around too much for your likiing, or if they were uncomfortably rigid when you fell face first into the floor. Dye has some fairly snug masks, with three different densities of foam, and they won't move much when you are biting a rat and trying to shake it to death. JT, on the other hand, uses much softer foam, that might absorb sweat more effectively and be gentler on your baby soft skin, though they move more than I like when headbutting someone.
How hard is it to change lenses?
Some masks make this very complicated. Dye Invisions are not fun to switch the lens in, though the Proto line is pretty easy. Some masks are designed to be very simple to disassemble, clean, and switch the pane in a hurry, while others are an IQ test to remove a scratched lens from.
Do they look stupid?
Like Mom always used to say, "take that thing off your face, you look ridiculous!" Aesthetics are highly personal, and it takes all kinds to make this crazy world go 'round, but if you are choosing a mask with full skull coverage for its looks, rather than its increased protection, you are hopeless and I wash my hands of you. Also, if you like the look of that JT FX-10 thing, well, I am pretty sure that we have nothing more to talk about about, ever. I can't hear you, Lalala-la-la!