I really like David Tennant. Actually, I've moved onto loving David Tennant now. Totally. But when the show comes back for its fifth season, I want an Eleventh Doctor. And I admit freely it's for one reason and one reason alone: Rose.
Rewatching the seasons, along with the new episodes, it became patently clear that Steven Moffat -- as talented as he is -- just doesn't really care about or want to explore the Doctor/Rose connection much at all. Which is fine; the show is not about the Doctor and Rose relationship, or Rose Tyler. It's about the Doctor. So lack of Rose and their connection is fine. Except when the whole last season and a half revolved around his feelings for her and to suddenly introduce a new character who has this deep connection to the Doctor ... oh, Moffat! You really need to read the scripts before yours. You really do. Of course, he may have this time, but I'm leaning towards doubting that since he didn't do so with "The Girl in the Fireplace." Which wound up creating a lot of cries of OOC because, oh the Doctor pretty much up and left Rose despite the previous episode -- as in the episode RIGHT BEFORE HIS!! -- being all about the Doctor promising Rose he WOULDN'T leave her. Sigh. Anyhoo, I'm getting off-point. My point is ... we're coming to the end of an era now.
Russell T. Davies is leaving after the fourth season, and Moffat is taking over (either the four specials or the fifth season in 2010, I'm not sure). And so with Moffat taking over it will be like a new era and I highly doubt that Rose will be mentioned much again (if ever), which, again, is fine. But for someone who does love the Rose/Doctor relationship, it will be a lot easier to deal with it and move on if it's a different Doctor, one who never had any relationship with Rose that we, the viewers, saw.
I've heard different reports about whether Tennant will return or not. Personally, as much as I love his Doctor now, I hope he doesn't. A new exec producer, a new Doctor, a new era. That's what I think will be best for the show (and for me as a viewer).
Donna can stay though. :D (Grumble, grumble, I know, I know Catherine Tate ain't sticking around. Grrr.)