Any 6/7/8 speed chain will work. Like you, I used KMC Z for a while, but I've been trying SRAM half-nickel chain lately. Too soon to recommend but so far so good. I've also had some failures: Clarks anti-rust (bad shifting) and Shimano HG (too worn in under 6 months) chains were poor for me..
However, if you're staying in the same gear and are seeing fairly rapid chain wear, I suspect you've probably worn the rear sprocket at least to the point where it's wearing the chain to match it pretty quickly. I'm surprised it didn't skip. When you hang a new chain on it, does it look like all the teeth are engaging fully, or is there some daylight beside the teeth? If there's daylight, it's new sprockets time - and change gear sometimes - if nothing else, your knees will thank you as you start off and the rear derailleur won't seize up.
Alternatively, if the sprocket's worn, you could just run it until the chain either skips or is really badly worn, but not too far because a snapped chain can be dangerous and annoying.
