I currently hardwire. I just find it easier to deal with than plugs.
I have used plugs (and my son still does). My choice for plugs would be the Corally (Trinity's are very similar). These work very well (at least on the battery) and still allow for a very clean wiring inside the car. I have not tried these on motors. I find that the placement of motors in some cars makes use of Corally plugs to be difficult.
As far as any noticable difference in available power: NONE!
The only reason to chose one over the other would be personal preference.