I actually just started watching in Season 5. Matt Smith is the first Doctor I saw. A friend of mine insisted I would like the show and was amazed I had not seen it before. So I watched The Eleventh Hour when it was on and when it was over I said to myself "How have I lived so long without this show!" From there I started watching the 10th Doctor episodes on BBC America but got tired of that and got all the DVDs for season 1-4 + Specials. I am completely hooked
That's pretty much where I am - I'd seen odd episodes Tennant first, then Eccleston but series 5 was the first whole series I watched also because a friend told me I would like it (he knows me so well!!!)