Could someone point me to a list that shows the tiers of different groups sets for stuff like Acera, Ultegra, SRAM, XTR, Campagnolo, Suntour, etc? I can't tell which is which and why one is better than the other ecetera. Also, how do you tell which ones are for mountain bikes versus road bikes?

My Diamondback Outlook mountain bike has a rear derailleur that says Shimano 7SIS on it and I have no idea what that is.

Thanks!