Well really, I'd rather have a McGann series than another Tennant series. I love Tennant and he was my doctor, but McGann got about 40 minutes screen time, he deserves more. Tennant is fantastic and I'd love to have seen him for longer, but I think it couldn't be as good as it ever was with him as THE doctor.
However one positive of this is that Smith IS leaving. Am I the only one who has become utterly fed up with Smith? I can't wait to see the back of him. His whole era has just been breaks in the middle of series, badly written series finale's, and underwhelming episodes in general. It's time to say good bye. At long last. And thank god. Smith did have some good times. Eleventh Hour, Cold War, The Angels Take Manhattan, and Impossible Astronaut/Day of the Moon come to mind, but other than that, most Smith episodes have been average at best, with the majority of them being under average or just plain shit. Hopefully Capaldi will bring a wind of change. he will be his own doctor instead of basing himself on the second doctor like Smith did. I don't want Capaldi to be the next first, third, or even sixth doctor, I want him to be his own doctor. I want him to be the 12th doctor unlike Smith being the next second doctor and Tennant to a degree being the next fourth doctor.
But really, people on this forum are forgetting one thing about Tennant's doctor. He has not just become a doctor, he has become the doctor. The default doctor. He's the Tom Baker of the 21st century. Not only does tenant seem to be based a tiny bit on Tom Baker, but he has pretty much become the most iconic doctor, especially in the UK. At the end of the day, Tom Baker and David Tennant are the default doctors now. Remember in the days of the classic series that Tom Baker was always the doctor people thought of when someone said Doctor Who, that's what Tennant has become. Plus younger fans have grown up with Tennant, me included.