Count me as one that voted for the AR.
Simply put it is a barbie doll you can do almost anything you want with. You could for instance throw on a dedicated .22 upper and shoot cheap. Conversely if the 5.56 round isn't enough for your needs you can easily get a 6.5 grendel or 300 blk that might fit your needs (long distance shooting or hunting). That's not even getting into all the accessories and customization options out there.
There's also a question of value and in this again the AR is light years ahead of the AK. Mind you it wasn't always that way as AK's were super cheap at one time but that's changed completely. Now you have what were $800+ AR's selling for $500 or less. AK's are not nearly as good a value and the more affordable ones oftentime are very rough (even by AK standards) and leave much to be desired.
SImply put you are getting way more gun for the money in 08/2017 for an AR compared to an AK.
As for the others, well, a 20 gauge shotgun is a very versatile gun. However unless shoot trap/skeet or have your own land, you'll likely be limited to shooting slugs at the range (most ranges anyway) and that is probably the least fun thing to do with shotguns.
So I'd say go for the AR all the way. It's tough to beat a quality factory S&W M&P-15 these days for < $500 or if you want to build your own and roll the dice a bit with assembly, a PSA model for even less.
The lever gun has appeal of its own kind and an aged quality that might be what you want. However as a round, it isn't exactly blowing away something like the 300 blackout in an AR. Plus the quality of some of the lever guns leaves something to be desired, especially Marlin models after the freedom group takeover.
Be sure to followup and let us know what you got and how you like it.