I'm thinking about getting a new fixie but wonder what size rims I should get. I've heard that deep v wheels are easier to handle then just the standard rim size.
The consensus opinion (for typical road use) seems to be Deep V's, apart from being best for showing off cool colors and looking good, have no advantage over other rims. Some people report they are stronger - break spokes and go out of true less often, although I cannot find a scientific study to confirm this. What I have read, people have replaced old, worn out, cheap wheels with new higher quality deep V rims, and then claim the Deep V's made the difference. The reality appears to be the new and better quality made the difference, not the deep V.
I have found no evidence that Deep V's improve handling, to the contrary, there are many reports of Deep V's making the bike harder to handle in cross winds - presumably due to the larger cross section of the rim.
Its not a big surprise that Deep V's and Fixes are commonly seen together - they are both products with more disadvantages than advantages for an average cyclist, promoted with evangelical enthusiasm by a few and ignored by most.
My fixie started out with Mavic CXP33 ("normal") rims. At some point I switched to Rigida DP18 rims on the same hubs. The reasons for switching were mostly style-related. The DP18's are not really "Deep V", but a lot deeper than the CXP33.
Subjectively, the CXP33 were weaker, i.e. went out-of-true more often, but a cursory google'ing showed that these rims seemed to be weak even compared to other "normal" rims.
I didn't notice any difference in handling, but that's not really surprising as my fixie is my commuting bike and the cities I lived in all had a lot of traffic lights, so building up high speeds was nearly impossible.
Having built a couple of wheels, I suspect building a wheel with Deep Vs and large-flange hubs really is a PITA. If using traditional three-cross lacing, the spoke-to-flange angles will probably be problematic, too.