What do you want to do with mod_perl? Are there any features in Apache or mod_perl 2 that you would find helpful? There's no correct version: it depends on what you want to do.

Version 2 is stable, but not yet released because the Apache API is still changing. This means you need to make slight chanages to your code between releases, which can be inconvenient. Most of the work going into mod_perl is for version 2: Version 1 is stable, mature and unlikely to change much.

If you're not already aware of it, take a look at the mod_perl Web site.