I have bog-stock Tourney derailleurs on a 21-speed, MTB-geared pedal-forward bike (an Electra) - the FD is top-swing, bottom-pull. They're combined with the SiS 7-speed indexed thumb shifters. The bike is an everyday, all-weather city commuter.
The derailleurs always seem to be going out of adjustment (tho it's better with the new shifters) - would upgrading the derailleurs help, or is this just how it's going to be with a bike that has such a long chain? Would one derailleur going out of adjustment affect the other? Do higher-end derailleurs hold their settings better, or are they just lighter/more durable?