Wheels seem to be the most sought after upgrade for road cyclists. In my opinion, there are a bunch of different purchases with more bang-for-the-buck than race wheels, but I can't deny the cool factor of deep carbon wheels. They will make the ugliest bike look pretty. When you're ready to pull the plug and buy some, there are a few key decisions you need to consider.
For triathlon and time trials, it isn't a very hard choice. Race a disc in the rear, or a disc cover if you are cheap like me. Run the deepest and fastest wheel up front you can handle. For road race/crits, the decision is more difficult.
The biggest is going to be whether you want tubulars or clinchers. There are plenty of purists out there that will tell you that you have to buy tubulars. They'll give you a list of reasons why. They will tell you that tubulars ride better, that they are faster, that they are lighter, and that you can ride out a flat.
In my opinion, only half of that is true. Yes, they are lighter. Quite a bit lighter in many cases. Do they ride better? It depends on your tire choice. There are clinchers out there that will ride just as well as tubulars and there are tubulars out there that ride like crap. The same is true when it comes to rolling resistance. Some tubulars are fast and so are some clinchers. A tubular probably is more safe to flat on a descent, but regardless of whether it is a tubular or clincher, you're still going to want to change the tire before the end of the race.
Then you need to decide how much you want to spend. You can spend $500 or $5000. In some cases you get what you pay for, but there is a point where you get very little return on your financial investment.
You have to decide how often you are going to ride the wheel. If you are only racing on it, are you cool with changing out brake pads every time you race? If so, you can get something with a carbon brake track. If not, consider a wheel with an aluminum brake surface. It will add some weight and hurt the aerodynamics slightly, but you won't have to worry with the brake pads each time you switch. Sure...it only takes a minute to swap pads, but some people don't want to do that.
If you are using the wheel every day, you'll want to make sure you get something with a quality braking surface. I bought a cheap Asian-made knockoff and I was amazed at how quickly the braking surface wore down, even though I always used the right pads. I wouldn't have gotten more than a few months of daily riding out of this wheel. The higher dollar wheel brands use a better resin that won't wear out as quickly. If you want your wheels to last, be prepared to spend some money.
With tubulars you are literally stuck with whatever tire you choose, unless you want to peel the tire off and re-glue it. If you have a flat, it costs a bunch of money to replace it.
With clinchers, you have the ability to select tires based on race conditions. Is the course well groomed? Use a fast tire. IS there a lot of debris? Take 5 minutes and put a more flat-resistant tire on. If you are doing an ironman on a course with broken glass and gravel, do you really want the same tire you use on a clean crit course?
The argument that tubulars can hold more pressure has been ruined too. A tire inflated to 160psi is actually slower than one inflated to 110psi unless you are on a perfectly smooth track.
The last question is what you want to get out of the wheels. If you want something that looks cool, the Asian-knockoff will look cool. If you want something fast, again, you'll have to spend more money.
I did some aerodynamic testing using Golden Cheetah's aerolab and found that my 50mm deep carbon wheel was slower than a stock roval wheel that came on a specialized tarmac. I was amazed, but I tested it again and again and the results stayed the same.
I was looking for the wheel that would be the fastest. I believe (and any calculator will agree) that aerodynamics trump weight in almost every scenario. The only exception would be an uphill time trial like at Joe Martin. I wanted to buy the most aerodynamic wheel. I looked at tests from pretty much every manufacturer. They all rate their own product as the best (obviously) but they almost all have the same brand in 2nd. Independent tests almost always say the same. Zipp.
I ended up buying a set of Zipp 808 firecrests. It's hard to argue with Zipp wheels. SRAM is the parent company, and I've never dealt with a company that had better customer support. IF I'm spending a couple thousand on wheels, I want a company that will stand behind the product like I know Zipp will.
I went with the 808 firecrest because the new firecrest design is supposed to handle better in the crosswinds, and the 808 is the deepest and fastest firecrest model. The firecrest rim is wider, and it comes in a clincher model that has carbon brake tracks.
I love these wheels, but if I had to do it all over again I would probably do the 404 front and 808 rear. It might not be quite as aerodynamic as the 808 front/rear, but the handling would be much less sketchy. The 808s are great in crits, but in road races with 40+mph descents, the 808s can be a handful. If you aren't a big rider, a more shallow front with a deeper rear will work together to provide more predictable handling.
I'm not saying Zipp is the only option. There are lots of other good companies out there. I think HED, Mavic, and Bontrager all make nice wheels; but for everything I was looking for, the zipp firecrest came out on top.