Well, this is for demoing, where I always start with a drum loop, but when I track in earnest I'll probably start with scratch guitar and/or bass to a click, then track the drums and toss the scratch tracks. That said..
For the longest time, I'd always track drum loops, then rhythm guitars, then leads, then bass. However, recently I've started recording bass first (after a drum loop, naturally) for a couple of reasons:
First, I always found that after recording bass I wouldn't be happy with how the guitars fit in with the bass, so I'd want to re-record rhythm guitars anyway. This way, I already know how they're supposed to fit together as soon as I start tracking.
Second, I'm a better guitarist than a bassist. Unintuitively, this is a reason for me to start with bass - hearing bass alone with no guitar around it makes slight hesitations really stand out, so if it's 97% perfect instead of 100% perfect, then I'll hear it clearly. Also, by the time I've finished everything else and begin tracking bass, I'll have been recording for quite some time, usually. As a guitarist, I care more about the guitars than the bass, so I'm much more likely to accept a sub-par performance just to wrap it up. The obverse isn't true for two reasons - one, that I do care more about the guitars, and two, that I'm just better at guitar, so I can usually nail a part in only a couple takes.