I can't choose.
There's my first proper bike – a 2003 Rockhopper that I kitted out with Hope Minis and sold to a mate who still has it. I get all nostalgic whenever I see it.
My 2004 Enduro, which I've covered thousands of happy miles on. I still have it, but it's in need of forks, wheels and cranks and lives in the garage.
My 2008 Rock Springs, massively entertaining and a very confidence inspiring. Compared to the Enduro it climbs like it's made of lead, is too short in the top tube for all day riding but is guaranteed to put a smile on my face. Since buying it last year I've only used the Enduro twice.