Shawndoggy, your world is full of great choices.
If you are really talking a single pair of REV 10's vs a pair of Deviants, then you are comparing 4 mid bass drivers with the Deviants and 2 with the REV 10's.
I have owned a pair of NVS Tyrants (essentially the same, just in the older enclosure) and currently have 2 pair of REV 10's. So my comparison would not be perfect, because I am talking about a 4 year old version on the NVS.
Here is my breakdown:
1. Customer service - Wetsounds is awesome. SO is NVS. I had a problem with my Wetsounds and TIm and company fixed it ASAP. When I had NVS, I even had Duane's cell phone number, and he was willing to answer questions I had, when all this stuff was new. It is a tie.
2. Hang height - nice bonus to NVS. I like the new clamp and enclosure style for the NVS. Limits the hang height on those big speakers.
3. REV 10 can rotate, nice feature. I have not used it yet, and honestly, not sure I am ever going to, but still cool.
4. Water resistance - I cannot speak for the newer NVS, but my older ones were made with paper cones that were treated with a water resistance coating. The new REV seem much more water resistant. I never have been caught in a big rainstorm in either, but the NVS made me a little nervous when thunderheads were off in the distance, the REV not so much. Maybe they have changed cone material since then.
5. Pure volume on either speaker is huge. No worries about your rider hearing these things. Riverrunner's thread is cool, but you could probably hear me screaming all the way across the lake on a calm day like that. I really want to know if I can hear it with wind blowing and 350 horses roaring in front of me. Both will do the trick. I am not sure why the comparison of Deviant to just 1 pair of REV 10's, but I think the nod on volume would have to go to a set of Deviants, since you have twice the midbass cone. WIth 2 pair of REV 10's, I would have to go with superior midbass projection on the WS.
6. Sound quality - usually not much of an issue, because the noise in and around a boat make it a terrible concert hall and volume will usually win out. But having said that, the REV 10's really do what everyone says and you don't get that ear piercing feeling that you get with the previous versions. The warmth of the WS speakers is incredible. I am in love with the REV 10's. After we are done riding, just relaxing around the boat at low volumes, the REV's sound better than my NVS did.
Again, these NVS were versions from several years back, not sure if he made significant changes to cone material, crossovers, etc since then.
Free wakeboard if you buy wetsounds from my dealer: http://www.automarinecare.com/