RE: best 3 1/2 inch gun
I've got two suggestions that haven't been made yet...if you want a good 3 1/2 inch shotgun under 500$ then look at:
1) Benelli Nova pump...a lot of guys I know shoot them and they are pretty much bulletproof. My brother got a camo one for Xmas and it ran him $349. That's a lot of gun for the money.
2)Browning BPS...the 3 1/2 Stalkers run about $450 and are as solid as they come. The camo ones will run you a little more. A little more expensive but you get what you pay for.
Don't rule these two out.