http://forums.mtbr.com/showthread.php?t=602215
If your shifter is actually broken, get whichever. I think the 7 and the 9 are both in the diminishing returns part of the line - good, and not a whole lot of difference between them.
You don't have to replace your rear derailleur for more speeds - it only "knows" how much tension is on the cable, and SRAM has used the same pull ratio for years. You do need a new cassette, and you should get a new chain if you're replacing your cassette, to get the most wear out of both (and because lower-speed chains are fatter than what higher-speed cassettes and shifters are designed to work with, potentially causing shifting problems and noise.)
I didn't like twist shifters when I had 'em, but I only had the crappy ones. Try a bike that has a set and then decide.
If your shifter is actually broken, get whichever. I think the 7 and the 9 are both in the diminishing returns part of the line - good, and not a whole lot of difference between them.
You don't have to replace your rear derailleur for more speeds - it only "knows" how much tension is on the cable, and SRAM has used the same pull ratio for years. You do need a new cassette, and you should get a new chain if you're replacing your cassette, to get the most wear out of both (and because lower-speed chains are fatter than what higher-speed cassettes and shifters are designed to work with, potentially causing shifting problems and noise.)
I didn't like twist shifters when I had 'em, but I only had the crappy ones. Try a bike that has a set and then decide.