For $300, if you don't get an 870...
...you habve serious problems. They are everywhere, and the 870 express is the best darn pump gun under $300 EVER.
I'm usually in the "get something original, everyone has glocks and Kimbers" camp, but there's a reason everyone has these guns. Mostly because of fads or marketing, but I've never seen an ad for a Remington 870, but every shooter I know has one or more of them. I have three.
Get an 870, please. That way you won't be back here on TFL trying to find accessories for a winchester model 12.