First, here's a good resource:
https://www.dcrainmaker.com/...in-depth-review.html Second, there's hard to find much fault between the big three (Qaurq, PowerTap, Garmin-now with the V3), it just depends on your equipment needs, budget, preferences.
I have a DFour on my Argon and I have nothing but great things to say. I had a Cinqo prior to that and it worked great. Quarq's customer service is a thing of legend, but I also highly support Saris (being from WI).
That being said, it really depends on your needs. I wanted to get into Rotor, but 2inpower wouldn't fit on my bike (Trek, at the time). If I had to choose again, I would go P1 pedals.