I voted Mossberg 500 even though I like the 870 better. The reason is a Mossberg is cheaper. Last year I was looking at getting a pump shotgun and really wanted an 870 but almost bought a Mossberg because of the price. Iv'e shot both models and had good luck with both, I've been hunting and used my FIL's shotguns and never failed to kill anything with them. His 870 the first production model 870 to come out so it's old but it still shots like a new gun. I've seen him kill rabbits at 100 yards with his 870. He also has a Mossberg 500 in 20 gauge and a Mossberg 600 in 12 gauge and both shot great.
I've never fired nor do I know anyone who has a Nova but I've heard good things about them. I did buy a pump shotgun a little while back but didn't go either of these 3 choices, I went with a NEF Protector pump. It was really a spur of the moment buy but it shots great and is an 870 clone.
Century Arms AR-15A2, 5.56
1946 Mosin-Nagant M44, 7.62x54R
1978 YUGO SKS, 7.62x39
NEF Protector Pump, 12 gauge
Savage Model 64, .22LR
NEF Pardner Tracker II, 12 gauge
Rock Island Armory 1911A1, .45 ACP
Remington 870 'Express Magnum' 12 gauge
Bersa Thunder .380