Raven NVX: Personally, I used to *LOVE* my raven. I thought it was way better than my flex 7... sat closer to my face, felt good, was light, easy to breath / yell. All kinds of good stuff. The lenses didn't tint as much as I thought they would, but I never had a problem with them. After a while, it looked like spots were appearing on the mask. I assume either this is paint staining the lense or some sort of problem with the lense tinting. Sometimes it went away, other times I was stuck with small purple dots on my lense. It doesn't bother you too much when you have it on.. you actually have to look for them but I don't see why they should be there in the first place. Anyway, after a while the foam started coming off the mask... foam glue didn't work to keep it on after playing with it, and I've yet to hear from Raven about working something out about it (ditto with their shin/knee guards). I plan on calling them sometime soon in the next few days and seeing if something can be done. (~$50)
Flex 7: I haven't tried a proflex, but my flex 7 wasn't too bad. Didn't fog, just didn't fit how I like them to. Sat a bit farther from my face than I'd like, but not a huge deal. Didn't fog and you could get bounces off the flex of the mask, though the chances of getting hit on the flex part itself is rather rare. ($30)
VForce Morph/Shield: The VForce Morph I've heard a lot of good things about... personally it just looks like the mask is too big and sits oo far from my face, though this is personal preference. The one thing that sets me off from it though is the fact that it's anti-fog coated, not a dual paned thermal lense. I've heard a lot of people say it doesn't fog, however, I'd really rather not have to worry about the coating washing off ... on the other hand, how often do you wash the inside of your mask? (Morph: ~$60 Shield: ~$40)
Proteus: I've heard good and bad things about this, just as I have the Invision (below). Namely the mask is small, and if it doesn't fit you just right (eg you have a big head) your chin sticks out of the bottom, esp if you open your mouth. I haven't heard any problems with the lense fogging abnormally, but the whole thing with the advanced hearing system is supposed to be BS. (~$50)
Invision: Simliar to the Proteus (above), the two main bad things I've heard are that the lense fogs (while others say they've never had a problem) and that their chin sticks out. I've heard the early Invisions had problems fogging and was quickly corrected by Dye. Much of what I've read on this has been good. It looks very ventilated at the bottom... if you get hit in the bottom of the mask, you'll more than likely be eating paint.. same as the Raven, though it also means you can be heard easier.
I'm not trying to plug any of these... since my NVX essentially broke on me, I've needed to find a new mask. All but the Flex 7 and Proflex were on my list of masks to look at (I already have a Flex 7). If Raven manages to pull through and replace the mask, I'll be selling it ASAP.. I'm not even going to try to deal with it (Burn me once, shame on you. Burn me twice, shame on me). Ultimately, I decided on the Invision. It has 3 stage foam which I can only assume is like the NVX (I haven't tried one on yet), has a thermal lense and is close to my face. The only problem I have with 3-stage foam (at least on the NVX) is if it gets wet, it's gonna compress.... a lot. At least my NVX did. Oh well.
Although I'm sure it's the last thing you want to hear, your best bet is probably to try them on and see which you like best. A lot of it is personal preference. Hope that helps.