Just stick with v8 zombies.
Crowbar issues that came with V8 (personally I'd just remove the crowbar).
Missing CI icons
Zombies keep jumping on top of each other and getting stuck. (I don't mind if this happens but it needs to happen less frequently).
Zombie/player damage doesn't always work
Zombies targeting player zombies.
Zombies getting stuck in big groups
Zombies don't break bricks sometimes
...Seriously?
There's more bugs in that than there are in gamemode_zombie holy stuff
On top of that, gamemode_zombie has many weapons/items (propane tank, pipebomb, healpack) bricks (ammo, health locker), functions (built-in ammo system, customizable director) and other content (zombies, downed/revive) that v8 zombies lacks.