Depends on how much you want to spend, and whether or not you have a bunch of wheels already. If no wheels, then a PowerTap will work well and a new one can be bought reasonably via Coach Rich and Wheelbuilder.
If you have a bunch of race and training wheels, the a Quark would be a better choice. Again, reach out to Coach Rich for a quote.
They connect wirelessy via the ANT+ protocol. How they do that....I don't know. I just know it works.
The Garmin 910XT is a great triathlon computer. It uses ANT+ technology to communicate with your power meter. I know a lot of people use PowerTap and are happy with it. My own 2 cents is I prefer the Quarq so that I am not locked into using one rear wheel all the time. When I race I switch to my rear Zipp 1080; when I train I use Ksyrium SL's. The only solution (I am aware of) if you have a power tap and want more "aero" wheels is to use a wheel cover. Just something to think about. I am sure others will offer their own opinion. The StagesOne power meter is also very intriguing, but not sure you can buy it yet. Also, if you do, you will be buying into a first generation product. But, again, it is a nice price point for power meters and worth considering, depending on your timing needs (how soon you want to buy it). Careful with the SRM. They are an industry standard, but I do not believe they are ANT+ compatible, forcing you to use their own proprietary head unit. The Garmin will give you all the basic TrainingPeaks stats, too.
High level, very general rules: 1 bike, multiple wheels is crank based choice - so Quark or SRM 1 wheel, multiple bikes is wheel hub based - so Powertap.
It's really easy to swap rear wheels between bikes, much harder to swap cranks.
I have PowerTap that I swap between road and tri bike. Most people I know with a Quark tend to put it on their favorite bike and ride without power on the other bike because of the hassle of swapping out the crank.
I use an aero jack on the wheel when racing. They are very aero. Check out data at wheelbuilder.com
Everyone I know with a power meter seems to like it and I don't hear many regrets about buying the wrong one.
I love when this thread pops up. I use a crank based unit because I change wheels a lot, deep dish, tubies, all around wheels, the works. Crank based makes it easy. Tom is correct above that changing cranks can be a pain, but it is still a "1 banana" job. You just need a tool or two and it helps to have bikes with bottom brackets that are "harmonized", meaning adapted so you can just slide the crank in. Go to YouTube and look up swapping cranks or changing bike cranks and you will see it is straight forward.
I went through this a while ago, and decided on a powertap built on flashpoint wheels (now sram 60's). Cost about the same as a quarq, and I figured that I would never spend the money for race wheels. they have been great wheels for both training and racing. Rich can help get you a good deal from wheelbuilder.
Comments
If you have a bunch of race and training wheels, the a Quark would be a better choice. Again, reach out to Coach Rich for a quote.
They connect wirelessy via the ANT+ protocol. How they do that....I don't know. I just know it works.
x2
If you tell us your budget and what your current gear situation is and we can try to help a little better.
What bike do you have? What components? Do you have race wheels already? But most importantly, how much $$ do you have available to spend.
Most newer powermeter will simply communicate wirelessly using the ANT+ format, so your 910XT will be able to be used for most of them these days.
1 bike, multiple wheels is crank based choice - so Quark or SRM
1 wheel, multiple bikes is wheel hub based - so Powertap.
It's really easy to swap rear wheels between bikes, much harder to swap cranks.
I have PowerTap that I swap between road and tri bike. Most people I know with a Quark tend to put it on their favorite bike and ride without power on the other bike because of the hassle of swapping out the crank.
I use an aero jack on the wheel when racing. They are very aero. Check out data at wheelbuilder.com
Everyone I know with a power meter seems to like it and I don't hear many regrets about buying the wrong one.
Check out eBay or Craigslist for deals.
You're good to go with the 910
If you haven't already, read Buying a Powermeter Through Endurance Nation (Gear Forum) and Before you buy a power meter (Wiki)
Blatant self-promotion: http://members.endurancenation.us/Resources/Wiki/tabid/108/Default.aspx?topic=Guide+to+Power+Meters
I believe this to be true, Tito.