eMule is pretty easy to set up, if I can anyone can. I can't set up BT, therefore the best answer to the question should have been the best is the one you can use.
Falling it depends on what your config is, cap ul/dl to a max of 80% of bandwidth any higher and you flood your connection. If you have a router max connections should be no higher than 250, and kad should be turned off. Remeber to give permission in firewall and forward ports for routers. In se3curity, under options, set it to accept messages frm friends only, that way you avoud spam.
eMules' own forum is a mine of info if you have problems, but I will help where I can. It depends how long ago you were talking even today people are mixing up eMule with eDonkey. There are various mods of eMule too, to fit certain needs, namely releasers and rare file holders, though that is another story and should not been gone into until eMule is running first.
As to rare files, I believe anything over a couple of months old is rare on BT, yet on ed2k network I have found files of things that are from the 80s and 90s. Not having the equiptment or knowledge to convert from VHS I had to find a copy of a film I have so I can watch it on DVD and to my suprise it was there as it has a limited market. The reason I needed to find it is my VCR blew up, literally, the cat peed on it he's never been near the TV since. I suppose that would make it hard to back up from VHS.