I love WDYTYA but am looking forward now to see some of Finding Your Roots, because I didn't know about it, thanks for the tip!
I think I've seen almost all of the UK WDYTYA! Some of my favourites are Alistair McGowan, Liz Bonnin, Boris Johnson and Alan Cumming. I've also seen loads of the US ones, but prefer the British.
To add to that, I've seen all of the Swedish episodes, and lots of the Danish ones. Still the UK ones are my favourites. The Danish one with farmer and tv-personality Frank Erichsen was fun.
UK WDYTYA FTW :-D