I'm sure you've probably seen this already, but the following thread gives something of an overview of whats out there.
http://www.cyclingforums.com/t/486931/garmin-vector-press-release
I posted it on that thread too, but we've just taken stock of our 2012 PowerTaps, so I am a little biased in that favour, but all said and done, I think it is an impressive and flexible system.
I'm hoping the latest Powertap releases will have addressed bearing challenges sometimes associated with PowerTap hubs... certainly the theory sounds good!
I wrote an (admittedly) salesy article last week on the new PowerTaps which you can read here.
http://www.koolstof.co.uk/index.php?route=information/news&news_id=7
As for your needs, that depends to a degree on budgets and intended purpose. Do you want to use it racing, or training, or both. Will you want to transmit the system from one bike to another, or will one bike suffice?
The benefits of PowerTap are that they can be transferred from one bike to another, so you can easily have power on all road based bikes. The negatives are that you are only a puncture away from not having power measurement (annoying in races), and that there have been some challenges around the bearing life, although from what I here from UK distributors, that may have been addressed now.
SRM are the original system and still a favourite of the pro's. The associated price tag makes them less popular for the privateer.
The pedal systems from Polar and Garmin are a little new to comment on, but if you like Look pedals and feel that knowing individual legs outputs could be useful, then they could be worth a look.