I am another Zipp owner (well actually, the cheaper American Classic version) and a shop mechanic who has worked on several pairs of Lews/Reynolds and Zipps. Here is what I would base my decision on.
1.) The Reynolds use White Industries hubs. They are getting better but still a step below most other aftermarket hubs. (Yea, I have a White hub too, and they work fine as long as you don't put too many miles on them and NEVER get them wet. Don't even sneeze on them. And their customer service SUCKS.) Zipp hubs are lighter and I have never had to rebuild one for anybody. (Both seem to have a lot of drag when coasting.) Advantage: Zipp.
2.) The Reynolds rims are stronger and the wheels are stiffer, but if you do have to true them you have to remove and then reglue the tire because the nipples are inside the rim. (A major pain in the ass unless you pay me to do it and I charge $50 an hour) Advantage: Zipp.
3.) I don't have any idea which wheel is more aero, but I would guess the Reynolds because of it having shorter spokes, no exposed nipples, and a taller profile. But the taller profile is a definite liability in crosswinds or gusty conditions. Advantage: Draw.
Add this to what has already been said and you should have plenty of info.