I've had the PowerTap and now have the Stages solution. I have two bikes with the same crankset so it allows me to swap the cranks. Allows me to use different wheels as well.
The iBike Newton looks good but needs a firmware upgrade to allow indoor trainer use and another option to send the data to your Garmin

All told the iBike would cost me ~$750
Stages runs about the same

The recently shown at Interbike 4iiii $399 solution is similar to Stages in that it's a strain gauge attached to a crank but you attach it to your crank using epoxy. DC Rainmaker did a review

4iiii?s Introduces $399 Power Meter, Precision: My First Ride With It | DC Rainmaker

Another option to wait on is the Watteam PowerBeat which is both pedals for $499

4iiii?s Introduces $399 Power Meter, Precision: My First Ride With It | DC Rainmaker

Good luck