I've used 115 several times and it's the main uploading site that the Chinese groups use.
That said, I'm often forced to use it because it's the only option. And while it's ok, I never liked 115 because most of the files have a time limit of like 30 days (1 month) before it's dead. This is why it's so hard (or sometimes impossible) to access a lot of the old Chinese uploads. It's possible 115 may have changed it a few months ago because they completely reorganized their website, but I wouldn't bet on it.
Overall, I wouldn't recommend 115. I only use it because I have to in order to access Chinese uploads.
As for the others, I'll also chime in. depositfiles does have rare stuff long after most other uploads have expired, but the wait time, the 1 download at a time, the buffer time in between downloads, and the overall slow speed of download are all a pain. I primarily used it the past for A Team's Breaker and didn't really like it.
MU actually has always been my preference because of it's fast download speed, but it's gone now. MF is a close second because of it's easy accessibility and simultaneous download, but the situation is looking bleak on that front. Hotfile and Rapidshare seems like it's ok for now, but both of those sites are way too liberal in taking down stuff. Not to mention, RS gives out your information. Filesonic for all intents are purposes is dead.
So many have been taken down that I don't even know which ones work anymore.