There are a bunch of styles out there, but I believe that it should have a thermal lens. I couldn't stand being on the field when my goggles used to fog up. When your on the field, there is NO taking off your mask to wipe during the game. (I used to do it, but I used to be a bad role model )
I've got a JT spectra 260 mask, which comes with a thermal lens as standard. I've had no problems, gives great ear protection and excellent vision, no distortion or fogging, great peripheral vision. I've not tried any other 'decent' systems so I can't compare, but I can reccommend mine to anyone.
I've got JT IZE and i'm well happy with them.I like the fact spares are very easily obtainable.and they don't see too badly priced either.if you can put up with red,brown or purple you can often get them cheaper.
I got some flex 7 IZE's too, also got a Proteus, both of wich are excellent.
As far as the Vforce goggles go, they're great as well. Look 'em up at www.diablo-direct.com
One thing I have to say about the Vforces is don't get them if you have a head that is big enough to have it's own weather system (like me), because they won't fit as well. The foam around the actual goggle won't touch your cheeks, thereby allowing the shattered shell of paintballs to spray into your eyes, when you get gogged.
If you have a normal(ish) sized head, they should be fine.