Underfolders absolutely suck to shoot. Sidefolders don't suck, but aren't nearly as comfy as fixed stock. For a target AK fixed stock is the way to go.
Never had an arsenal so can't say first hand how they are. Furniture is cheap and not difficult to swap. A milled receiver will be noticeably heavier, and won't appreciably increase performance although it will feel less janky in your hands.
Why do you want an AK over a different platform? If you know what it is and realistically expect AK performance and ergonomics, you'll be happy. If you're expecting AR ergos with rem700 accuracy and HK quality, prepare for disappointment.
Whatever you get, check for canted front sight block, where the front sight is adjusted to (at windage/elevation limits) and double check all screws/rivets/etc for tightness, seems like more AKs slip through QA than others.