Different folk have different tastes. I know Heather & Anna prefer f/f and don't like anything masculine on either side of the slash. Me, I like most any combination other than f/f or m/m, and I've done a sizable minority of f/m stories along with my m/f ones. I know some people just don't care for /m, no matter who or what the tickler is, and I'm sure some don't care for /f in the same way.
There's one variant that seems to be really under-represented, though 😀 That's /* tickling where the ticklee is a genderless Thing. Where are the mf/* stories where a couple gang up to tickle silly a poor asexual computer or alien? 🙂 🙂 🙂