So far Bittorrent >> * (with Azureus being my #1 client). Of course it's helped by having sheer volume and content variety on its side among all p2p protocols.
KLite K++ is good too (provided you could somehow get it ) but prone to corruption. It's superior to DietK which feels a tad too unwieldy (it's basically a band-aid on top of the spyware-rich Kazaa).
As for Overnet, eDonkey sorry but I've to say they suX0rs big time in terms of connection speed. For all I know it could be one of their esoteric network configurations that I did not tweak right, but I could no longer be bothered.
Never tried DC++ before.