Lube or spit?

Spit. Lube can work too well, and if it's really slippery then I'm just going to keep slipping off the hole when I'm trying to get it in. Once things get going precum keeps things gliding smoothly.

Straight guy, so top.
 
Prefer lube, spit will do if no lube is around - always condoms! Vers-btm at the moment

Oh that's an important distinction. I've only ever done anal with a long-term girlfriend, and we were monogamous and tested so we went bareback. Without the natural lube coming out of my dick, I'd probably need to use a bottle of lube.