How do you choose a film developer to use ?

Honestly, my developer choices have mostly gotten lazy. I keep a bottle of D96 working solution and replenisher in the fridge and almost every film goes into that. It's cheap, stores well, and bulk rolled double x looks best in it.

I only tend to branch out if I'm looking for a specific attribute (e.g. better pushing) or know a specific combo I like (e.g. fomapan 100 in rodinal)

I only use 3 developers for film: Rodinal <100, HC110>100, and D76 home made(rarely) for anything. Keeps things simple. For printing, I tend to like higher contrast negatives, these choices fit well with that. I use Rodinal almost exclusively at 1:50, though. The availability of REAL HC110 worries me, though, as I haven't tried any of the "new" ones due to having a large stock of "old" HC100 which I have almost run out of now.

@Michael Howard

These 3 are really a very versatile trio. The new HC-110 has lasted many years for me without problem, working like new, even though it has crystals/solids in the bottle. When I bought it, it was already expired and on discount. I don't take any special precautions.