i'm not sure, maybe Blender? that is also a free one and is capable of tons of things. or maybe Modo, but if you're an autocad guy then maybe Rhyno 3d is better for you i dunno. it's also a less graphic, more of a 3d design software, but is very user friendly as far as i know.
but don't be afraid of the frustration of learning a new software. if you let this fear own you and not letting you learn a new software, than it's gonna be even harder to learn new things. if you say it's too hard for AC to handle thing you wanna do than maybe that's the thing holding you back
try a simple modelling tutorial in 3ds max, maya, blender or zbrush and after a smaller success, you will be able to do bigger and bigger things!
just learn from others as much as you can!