If you're running off batteries or solar, the Trick-L-start is better because it doesn't do a 12v->120v->12v conversion. If you're on shore power or generator, the float charger is better. IMHO.
Edit: I guess the Trick-L-start can also be permanently installed, while you're going to have to connect the float charger when you want to use it. I think.
Don't need either on my coach because we have a BIRD to charge both sets of batteries from the inverter/converter.
2008 King Aire 4562, Spartan K3(GT) w/ Cummins ISX 600
2014 Jeep Grand Cherokee Overland 5.7L V8 Hemi w/ Blue Ox Aventa LX Tow Bar and baseplate, SMI Air Force One brake