You can pretty easily use most any 6-9 speed derailleur. My hybrid uses a early 90s 7-8 speed XT derailleur with a XTR 9 speed shifter and a 11-32 9 speed cassette and it works flawlessly. I have also seen plenty of friction set ups that use all manner of derailleurs so you should be pretty good with most anything however I would probably keep to Shimano because Shimano is just better and some may disagree but they are certainly all wrong