these are difficult questions to answer because so much depends upon persoal tastes and preferences.
literally, ALL of the pre-ban ak's are worth owning with the exception of the american receiver/chinese part b-west rifles.
in folders, you have a choice of norinco right-side folders and traditional underfolders. the chinese polytechnologies are also available in underfolder style.
both are excellent choices in the $800-1200 range.
a very few maadi egyptiam ak's were imported. they command very high prices due to rarity.
also avalable are the yugoslavian (stay away from the post-ban m-90 underfolders) underfolders. these are top shelf and also fetch a pretty penny. expect to pay $1500-2200 for one.
underfolders tend to loosen up and wobble a wee bit with usage. they also offer an odd cheek weld and are hot/cold on the face to go with the weather they are exsposed to.
the sidefolders offer a little bit better cheek weld, but are less desirable among collectors.
the norinco model for an underfolder can be an aks, and akms or a 56s1.