oh man this is an easy one.. it is simple..
the one that kills turkeys..lol
really i have killed birds with a single H&R 12 guage, mossberg 500, mossberg 535, mossberg 835, remington magnum 870, and remington 870 super mag.....
all of them did fine jobs. bottom line is you do not need to worry about the brand of gun you choose but rather you need to woory about finding the choke and shell(shot) combination that works the best in what ever gun you choose.
you can simplify it a little though. it seems that remingtons really like the indian creek and primos jelly head chokes.. mossberg 835's love them stardot chokes if you can get your hands on one and they are out of production and ppl just dont like to give them up. hevi shot seems to pattern alot better than lead but you can get killing patterns in about any gun with lead with simple tinkering to find the right combo.