Best thing to do, hit a couple and see for yourself.
If it was down to me, I'd go A Custom everytime. Z's are heavy and hard and have more tendacy to break than A's.
I personally think the tone of an A Custom is nicer and it will also serve you in more musical situations than a Z. If you buy Z it's going to be for very heavy rock, simple as. An A Custom could cross genres to funk, jazz, pretty much whatever you like. So if you want that flexibility, go A Custom.
Right now I use an 18" K Custom Dark Crash and I generally play heavy rock. I like it so why not?
i bought an 18" a custom projection crash and an 16" a custom fast crash not long ago. i put em next to some z's in the shop and they blew them away. so much more versatile. i play in a metal band and a pink floyd cover band works both ways haha