^ What auntie said.
In the last 2 cases, I knew little about either Tennant or Smith before they began. So I suppose I was treasuring the last moments of Eccleston and then Tennant respectively more than I was looking forward to their respective successors.
However, while Smith is actually my favourite Doctor, I do know a lot about Peter Capaldi and am looking forward to seeing his Doctor, even as I dread Matt leaving. My sadness at Matt's departure is tempered by the knowledge that Peter will be great. Although both David and Matt were of course great, I didn't know enough about them when they first were cast to have that sort of confidence in them.