I heard alot about the 18-200mm VR lense, but will it suffer at wide angle compared to the 18-70?
The 18-70 has a picture angle of 76° - 22°50' and the VR 18-200 has a picture angle of 76° - 8°. So you get exactly the same "wide" angle at 18 mm.
Make sure you read Gordon's comparison here
. Also, you can see Nikon's site for their technical data on the 18-70
and the VR 18-200
I don't know the first thing about housing for underwater photo, but be aware that the VR 18-200 extends to about twice its size, when zoomed all the way to 200mm. The 18-70 also extends when zoomed, although very little.
Also, be aware that the VR 18-200 will change its focal length by itself (i.e. the barrel will extend/retract), if you operate it at an angle, because of its weight, possibly causing it to loose focus. This will be a problem if you put the camera inside a housing and have no means to physically restrain the lens barrel.
For the underwater shots - and only for those - maybe you would be better off with a prime, such as a 50mm
or an 85mm
PS: Gordon, where are those primes reviews you promised a while ago?