It's worth looking at the reviews, granted there are not many for Stages yet but a google search on DCrainmaker is a very good one. His updated review had stages very positively ranked against the others. Many will say that the challenge is that Stages is not time tested yet, which is true but you gotta start somewhere.

I have the Stages and have been very happy with it, especially because like you I didn't want to change my crank and I didn't want a Power Tap since I swap wheels often. I really like that I can do any software updates via Bluetooth. As mentioned it does rate favorably against the others even given that it's only recording one side, I would say that the few times where I've done drills with one legged pedaling that I would have liked to see how my power compares from one leg to the other which obviously cannot be done with the Stages. A small thing but still...

The only other unit I would have considered was the SRM because keeping the appearance of my group was important to me but just couldn't justify the price as a recreational rider making a first foray into training with power.