As far as gauge goes it depends upon how much current/wattage you plan to run through it and the length. Example:
Having too large a gauge is better than too small a gauge. Then again, you don't want to string 10 AWG wire to charge an Iphone.
I'm sure someone will skewer me for this but IMO most wire is pretty generic and electrons don't know/care what brand your wires are but the insulation can matter. (There are special application wires like spark plug leads where I do think brand/quality matters.) The most important thing for vehicle wiring is to make sure you're using stranded, not solid, wire.
I like Posi-Lock products too although officianados here will tell you that properly crimped butt connectors are better.