eDonkey because I think it has a much more user friendly set up/skin/layout, plus has access to both overnet and eDonkey server networks (= more sources)
Overnet is a edonkeynetwork built in the Edonkey client alone. It used to be a stand alone application but is now built in the Edonkey 2000 client. Regular ed2k is serverbased whilst Overnet is a distributed searchable serverless network but it is still ed2k!.