i own them all and have tried each one on and off for the last couple of years. i like each one in its own way (and, also, am friends with guys at each place)
if you're just getting started and you aim to keep it light, then i'd start with the withings scale. you leave it in your bathroom, set your goals, step on it when you feel like it and watch trends and alerts from time to time. i find my weight tells me more about me over time than many other metrics: it shows my bad weeks from my good and, in indirect ways, shows when i stress out and get bad sleep (and therefore, end up eating poorly and exercising inconsistently)
I've had several Fitbit's and own the Withings scale; love them to pieces. My early Fitbit's broke when I sat down and caught them on the arms of a chair (once at a beer garden, natch) but the new Flex bracelet is incredibly nice.
if you're just getting started and you aim to keep it light, then i'd start with the withings scale. you leave it in your bathroom, set your goals, step on it when you feel like it and watch trends and alerts from time to time. i find my weight tells me more about me over time than many other metrics: it shows my bad weeks from my good and, in indirect ways, shows when i stress out and get bad sleep (and therefore, end up eating poorly and exercising inconsistently)