For under $400, you can't beat the 590 or the Remington 870. I am very pleased with the tight groups I can achieve with my out of the box 590. The 590 will hold 8 shells in the tube, and you can order it parkerized (black finish) to resist wear or rust. I've spoken with some 590 owners who have had feeding problems with the optional speed feed stock.
After I bought my 590, I ordered a Sure Fire foreend (a must, I believe, for any long-arm home defense weapon), and was shocked to find out that the bayonett lug blocked the SureFire light and thus prevented racking. My gunsmith milled the lug off so that it racks fine; guess I won't have to stab any intruders to death.
:-(