Recommend Crank-Based Powermeter for BB30 Ui2 Compact

[415brian]

I have a new bb30 frame (BMC TM01). I want to run compact rings (50-34) and 170mm crank arms. I'll be running Ultegra mech to start and then switching over to Ui2 TT as soon as its available.

I want to optimize for good front shifting with the Ui2. Which crank-based powermeter and rings do you recommend? Any significant difference/benefits between native BB30 crank vs GXP/hollowtech + BB30 adapter?

I've had good experiences with Quarq in the past, but also open to other suggestions.