Iron Wolf for sure, when it was announced it was being removed I remember a lot of people saying good it hurt me blah blah blah. I personally found it to be a pretty smooth ride, then again it might have been because i'm young and spry.
Also Demon from the same SFGAm it was my first looping experience so it has a close bond with me. It still one of my favorites not as much for the ride but the scenery around it. A lot of cool tunnels and rock structures, plus it has it's own theme song (even thought it's not played much anymore). I know that it will be on the chopping block if SFGAm looks to build a newer coaster, but i'm having hope that if in the future the decide they want to build a premier launch, that they will use the former structures of the Demon, maybe even called it the same name.