What, in your opinion, makes a really good rp partner? Have you ever dropped a partner you considered great, or kept a partner you didn't? Why?
For me, being a really good partner means you:
add to the plot in meaningful and dynamic ways
have decent, distinguishable characters
are consistent
For me, # 3 is important because I like routine and I like to get excited for my rp. If I know when to expect it, I can clear time to reply. I worry less about whether that reply is coming. And my expectations don't get disappointed. But I know a lot of people (heck, myself included) can't keep to a super regular schedule.
I have dropped good partners before because our writing styles just weren't meshing, and also because I just got too busy and I don't like rps that are only once-a-month replies. Or I just lost interest in the genre (rare, since I know my tastes, but it happens).
I have kept on partners who are not consistent, if they were exceptional writers and I loved the plots we were writing, but I usually peter out eventually with those.