I have a Mossberg 500 12ga and love it, ive had it forever and hunted everything with it and its never jammed, misfired or let me down in any way, and it'll take a turkey just as easily as it'll knock crows out of the sky...
a couple things I don't really care for though is that it has the rattle at the forestock/cycling arms that most all mossbergs seem to have, which may be an issue you might want to look into before buying one specifically for turkey hunting, another is the physical size, which has nothing to do with the gun itself and is probaby just a personal gripe of mine... many years ago I bought a Remington 870 youth 20ga for my son, and he didn't take to it, so I starting using it, and even though im a pretty big guy it actually fits and shoots great for me, I do a lot of brush pounding for various small game and when I use a shotgun that 870 is it hands down, it works excellent, which drops my big 500 12ga down to a crow/turkey gun
I do own both a 500 and an 870, and like them both, but its hard to compare them in too many ways as theyre two totally different guns, I like the safety on the Mossberg better, and Mossberg does have a 20ga youth model, but I already own the 870