I didn't like Catherine Tate's sketch shows, and was dreading it when she was announced as the Doctor's companion. I was pleasantly surprised to find that she was great in the role, and she did become my favourite so far.
Actually, none of the above. My favourite companion was Ace from the classic series, followed quickly by Sarah, K9, Jamie, and Romana. The best new series companion was Donna.
Honestly, I'm ambivalent and somewhat philosophical about this news. On the one hand, as a fan, I don't want the series to be cancelled again, and the 'competitive tender' thing might end up being a disaster anyway. On the other hand, fifteen seasons and a plethora of specials over a period of over two decades is a damn good run for a TV series, and the show had been showing signs of being tired as far back as Steven Moffat's tenure on the show. If it has a (preferably) temporary rest, then maybe that's for the best. It's not like Whovians are hurting for material to watch, listen, and/or read. I have a HUGE backlog of Big Finish audios to listen to, never mind my collection of the Virgin and BBC Books novels...