I would also recommend a gym over a bowflex, but for slightly different reasons.
Basically, any machine workout is going to be fairly limiting. Most of them tend to isolate certain muscle groups to work them exclusively. This is fine when you're getting started, but evenually you're best to move on to free weights and functional exercises that provide much greater challenge by working whole groups of muscles at a time.
If you have the money for Bowflex, you are likely better off investing it in a good gym with a good trainer to show you the ropes and get you off and running.