Here's my $0.02
Arsenal SLR 106f 5.56 AK - I have one, SUPER FUN to shoot, ammo is easy to get, but mags kinda expensive.
Saiga 12 pistol grip converted - Don't have one, but I don't like shooting shotguns (other than for hunting). Pretty limited use here anyway.
Robinson Arms XCR 5.56 OR 7.62x39 - cool gun, but for the money I would probably get something else.......maybe a SLR 101 milled with $$ left over for ammo/mags
Benelli m4 - meh.....another shotgun.......
Shrubmaster ACR - I'd get 2 guns for the $$ instead
ar15 di? piston? - If you don't have a AR yet, somethings wrong with you

But seriously, if I didn't have one, I'd go ahead and get a decent DI and be done with it.
At one point I had a bunch of AR's. I sold all but one because IMHO they are boring to shoot. I'd rather shoot a AK, FAL, PTR 91, or my pistol caliber rifles.
If you already have a decent HD gun, buy whatever you think will put the biggest smile on ur face.
