In reply to Luke90:
My phone (Samsung) really dislikes even a trace of water in the charging port, and even in a nice dry house can take an hour to stop grumbling (ie refusing to charge).
Obv it depends what you are doing and why you want a powerbank, but one of the main reasons I carry a powerbank is so I can be confident I'll have a working phone. The critical window is connecting the cable to your phone. If it is wet then charging may fail. It depends where you envisage charging things (somewhere nice and dry) and if you are happy to risk not to be able to top your phone up.
Yes you need cables to charge alot of things and are simpler, but the technologies usually coexist in the same device (ie you have a choice of mode). If it is dry obv use a cable.