I think all noteworthy has been said already.
I must add (like Dark Hunter already mentioned) that indeed Gundam fans are divided with their opinions on which show is watchable/good and which are not BUT then there are those like me who like almost all of them and don't think UC timeline is waaaay better than the others.
I thought that UC timeline had a bit too much drama to my likings, "Kill 'em all" Tomino really earned his nickname.
Nevertheless it is a good thing that some shows won't polish things up and keep it... err... "real". But it's a matter of opinion.
Granted all Gundams have some amount of drama and death, that's for sure. But UC makes to the top of that list hands down

That being said, I really enjoyed Wing, SEED (even Destiny... yes, you can stop gasping now), G Gundam (oh boy this was a blast

) etc.
So do start with the UC timeline, but don't yet throw away the alternate universe series either. Pick one and have a couple episodes to see if it's for your liking.
I'd recommend Wing or Gundam X or even SEED.