Power measurement is a funny thing. Depending on how you use it, you may be a slave to watching it and never push past your limits, or you might die a thousand deaths trying get the numbers just a bit higher. I fall somewhere in the middle, using a Quarq power meter to do it.
I've used power for years now. I remember my first 20 minute power test. It was when I was training for triathlons and would consistently be in the top 10% for the fastest bike split; I thought I was hot stuff. That test was so incredibly hard, and afterwards, the truth hurt: 3 watts/kg for 20 minutes was all I could manage. If you are unfamiliar with power numbers, I'll put it to you this way: pro cyclists can push about 4.4w/kg for 5-6 hours!
At the time I was using 1 wheel for everything. Training, racing, it was all the same set up. So for me, using a PowerTap power meter made perfect sense. It was bomb proof, consistent and never gave me problems.
When I changed over to just bike racing, I investigated some other options. I changed from having 1 set of wheels to a few, and with that change, I opted to buy a crank based power meter from Quarq.
These days, if a company stands behind their product regardless of what happens to it, you know you've found something special. That is precisely what I've found with Quarq. If I have had questions or issues, Quarq have rectified it quickly and painlessly, no questions asked. They value everyone equally which is refreshing. I once had a small issue with a unit and had to send it in for service. They turned it around on the same day and overnighted it to me so that I could have it for a race that weekend. It doesn't get better than that.
Aside from their service, the unit is awesome. I've had their older S975 and now their Riken, and both are fantastic. Compared to a PowerTap, they are featherlight, only adding about 125g to my crank. It communicates great with every ant+ head unit I've owned and most importantly, it is consistent. The entire point of having a power meter is to compare data. If it changes, you've got a very expensive magnet on your bike.
You can tell Quarq values their user a lot based purely on the design of their units. The battery is easily replaceable (without a tool!), the chainrings can be swapped easily without needing to recalibrate the unit, and they use a single bolt to remove the entire crank from the bottom bracket! In a matter of 5 mintues, you can change the battery, swap from your road rings to cyclocross rings, and install the crank on your cyclocross bike. Instant power.
I use Quarq because they make a great product and care about every one of their consumers to boot.