I am kind of curious what it is that draws you to one site over another.
I, of course, always post my mods at GHF. I think it goes without saying that I would put mine there as it gives me utter control over them.
I also always upload to PES. I have a few reasons for this:
1. Back when PES was the Summit, it was the first major mod site I used to collect mods.
2. I used to be a database admin there, so I had similar control over them as I do at GHF.
3. They have relatively fast and reliable servers. There are some network issues from time to time, but that is the nature of hosting in general.
4. The other sites just never appealed to me for various reasons.
Things that I have always felt important for uploading and downloading mods:
1. Ability to include screenshots when applicable.
2. User feedback system (although this can indeed be a two-sided blade.)
3. Ability to update available files.
4. Friendly and approachable administration (which is definitely why I personally avoid one of the larger mod hosts around.)
What do you hold to be important?