I have just started using xolox, and I like it a lot mostly because it tends to start downloads right away. It would be good though if it worked a bit more like edonkey2000 (www.edonkey2000.com)
edonkey makes a CRC and filesize of a given file and then makes a identifier out of that.
So if people rename the file edonkey still finds the files with the same content. I am still trying out which one of these 2 programs I like more

have fun and share