Well it all depends on what kind of story you would like. You could start with the original series or the movie of the series of Mobile Suit Gundam and then go on to the rest of UC in chronological order and then jump to one of the other series. Or you, having started with Gurren Lagann, could go right to G Gundam, Gundam Wing, and 00 with them being the slightly more Super Robot-ish series.