Synty's "Polygon" stuff is really nice, but doesn't have the "quantity" of vehicles I'd like to match the "quality." The "Simple" series generally has a lot more choices, especially as they've been doing that for so long. I have those same Evozon Battle Cars (all three kinds) and love how they look... I just wish there were more cars that matched that style.
On that note... This just came up:
https://www.assetstore.unity3d.com/en/?stay#!/content/130909