It is probably a good idea to gain experience in both online and live play. Being that you said you don't have much time to play poker in general, I'd say play online for now. Depending on where you live, you can jump onto a poker site
at any time of the day or night and find a game going on (USA has less volume since the black friday fiasco of 2011 hence the "where you live" proviso). Not only that, online play is much faster than live play so you can get a game done and over with in two hours or less depending on the blind structure you decide on.
I think live poker has its benefits too: for example, you are forced to sit and contemplate a bit longer during each hand: so you may give more thought and mental attention to hands you play at a live table just by the nature of live versus online play. When you play online, you are often making decisions in an instant and so may not be dedicating enough grey matter to your online play.
And of course, when you play online you use a wealth of information about players that is simply not available when you play live. Many would say, however, that the opposite is true as well for live games (though in the case of online poker we are talking more player statistics while with live poker we are talking more player tells).
So it is probably a good idea to get some experience playing poker online and live. Of course, the future of poker does seem to be online so I wouldn't advise just playing live!