The normal career path is from CFI to 135 to 121.

There are however some good jobs in 135 that would be worth leaving a regional (or maybe a major) for. 135 covers a LOT of different types of flying operations:

1 man, 1 airplane charter (Piston airplanes).
Night Freight (pistons singles, twins, a few turboprops)
Small/medium local charters companies (king airs, bizjets)...these jobs can be good, bad, or ugly.
Large Fractional Operators...these are jobs decent, but not spectacular.

The quickest way to a fractional is probably some RJ time at a regional.