I have four bicycles. The one I ride to work is a modified Trek Pure, but I had to modify it considerably as follows:
long handlebar stem (I like to stretch out)
172.5 cranks (had 165)
44 tooth chain ring (had 36 or 39 or something)
9 speed sprocket (had 7)
shift levers (had twist grip)
power grip pedal straps (sometimes use SPD pedals)
Toploader 3 carrier bag
The Pure has a slightly pedal-forward design and much less than a recumbant. For commuting it's excellent because it's easy to put feet down and start off again. The way I have the bike modified, with the slight pedal-forward design I end up being in the same riding posture as my road bike, except my entire body is rotated a few degrees. I use the same muscles and my knees come just about as close to my chest. Because it's a surprisingly light bike, even with fat tires, fenders, carrier, and bag, I can go almost as fast as I can on my road bike. Sometimes I take it on rides with the group and keep up just fine. The problem is, with pedal-forward, my weight isn't directly over the pedals and I don't have as much power, and I have to spin more which is probably a good thing. The flat handlebars and long stem allow me to stand up easily, which was impossible as it was originally, but I don't on this bike.
Anyway, I need to replace the derailleur. It has a cheap Shimano Tourney and the spring isn't very strong. Shifting is also very sloppy. It's the same derailleur I had with 7 speeds. I only have one half turn tolerance on the adjustment knob to have all the gears work, and on some it makes a little noise. If I go over a bump when shifting the chain may jump off the front chain ring, and sometimes it jumps off if I shift too fast under a load. That's pain if I've pulled out in traffic. Because of the pedal-forward design the chain is longer than normal, but if the spring was better there shouldn't be a problem.
My main road bike is a Giant TCR with Ultegra stuff. My other road bike is an old Seaki which I've made current. Both these bikes shift real well with no chain noise. I would like my commuter bike to be the same way.
I looked at several places online and have no idea what derailleur to buy. The Tourney has a long bottom portion with a large red wheel which I don't like much, anyway. Prices at Amazon are really good, but if I bought there the derailleur would come from a participating seller.
Any help would be appreciated. Thanks