I just picked up S&Ws FPC (the folding carbine, not the Response) and I'm liking it a lot.
With my Sub2k I put up with a lot of it's issues like trigger & ergonomics for the folding capability, the FPC would be a fine carbine even if it didn't fold.
Although the Sub is still quite a bit smaller & lighter than the FPC so a Sub can share a laptop case with a laptop or fit in a backpack without taking up all the space, while the side folding FPC is pretty thick.
If you're looking for an AR pattern, the Stern adaptors have a pretty good rep. I had several different 9mmARs but eventually let em go, just too big & heavy compared to my other PCCs.