Wow, thank you all.
I'm going to go with the KMC chain. By the way, why is an 8-speed chain the best choice for a 6-speed freewheel?
I once detached the VX RD before and reattached it, so swapping out the Shimano and reattaching the VX should be something I can do on my own.
If I do end up getting a new freewheel, which Shimano hyperglide do you recommend?
Also, as for the shop it was Rollin' Cycles in Washington DC and they closed a few days after I got my bike back. Good riddance! I'm particularly annoyed because my bike was spotlessly clean when it went in; when they gave it back to me they'd gotten grease all over the frame. I'm going to wash and wax the frame all over again.