I don't think these two gametypes have anything in common other than the fact you can use reqs so I don't like that they both have warzone in the title.
That said, warzone assault is the far more streamlined gametype, and is far closer to being a finished product than warzone is. Warzone feels like a sandbox where you can go frolic as you please, but it's very easy to lose interest in the goal mid game, it's probably one of the first multiplayer FPS gametypes where I've ever wanted to quit not because of rage, but because I was actually bored mid-game. I think plain warzone would benefit greatly from even more players, and yes more AI type stuff. But, the whole AI aspect of it is sort of boring because it's the same guys showing up and standing at the same spots. It's almost just a race to complete a checklist more than an actual combat scenario.
I dunno, I'm not into regular warzone at all. Assault is an actual quality gametype.