Recording- How do you come up with your Bass-lines?

[Bobbo 77']

Hola,
Question. When recording Bass tracks for tunes, do you Cat's go with the first bass-line idea, dictated by the tune, or do you write and re-write the lines? I'm presently working on a project for a Guitarist-songwriter in which some song's require sequenced music which I do for him. Usually most client's have an idea of what type of line they hear in their tunes, but here I have Carte-Blanche to do my Thang. Just curious how the rest of my Bass playin' Brother's come up with their ideas!
Bobbo 77'

[pretaanluxis]

I always re-write many times, keeping only the best stuff. Generally I like to keep the root notes and the groove solid, but keep it interesting by adding little fills imbetween when the other instruments arn't too busy.

[Vorago]

I have ideas I play around, but my basslines are rarely 100% fixed.