Hmmm, not sure if this starts with a 'proper' bike, but it was all my parents could afford - bless 'em
1993 Townsend Warlord (it had elevated chainstays )
1997 Trek 6000, later completely upgraded, ended up with Bomber Z4s, Hope Mono Minis, bargain bin XT/XTR bits, proper wheels etc.
2001 Viper frame with many nice bits from above.
2003 2nd Hand (1998) Sintesi Bazooka frame with evolution of nice bits, Viper becomes a SS
2004 Giant AC with further evolution of nice bits - stolen 1 month after building
2004 Giant AC, Viper becomes commuter
2006 Specialized Langster, Viper becomes 'pimp' SS
2008 Specialized Tarmac
2009 Bionicon Ironwood
2010 Genesis iO frame for the SS.
(then I left the bike trade...)
Still own the last 4, and they actually get about the same number of outings.
Best bike? The bike I spent the most on and loved the most through it's life, probably the 2004 Giant AC, it ended up with Boxxer U-Turns, full X.0, Hope M4s, spangly wheels and finishing kit. It died when a bearing wore out after 5 years, and was completely seized into the frame. It took months to get fixed and sold, in which time I bought the Ironwood.
The Genesis iO is probably the one I'd keep if I had to choose but one. I've had so much fun with this one, rode actually thousands of miles in the USA on this when I wasn't working.
Most expensive - Bionicon Ironwood. I have a love-hate relationship with this bike. When it works, and in the right place, it's brilliant. But it needs constant fettling and I live in the flatlands :-(.