Really depends what you are going to end up using your shotgun for. If it is solely fox drives, then a semi-auto and perhaps one that takes 3.5" cartridges will cover all bases. What's more, there's nothing wrong with a synthetic stock there and you can get them with a mechanism to soak up some of the recoil of the big cartridges you might use. A Beretta Xtreme would do nicely although there are cheaper alternatives and a 3" chamber would certainly suffice.
However, if you want to cover all eventualities then go for an over and under sporter with multi chokes. You can then use it for your foxing, clays, rough shooting, vermin control, driven shooting, hell, even accept that day at Sandringham with it. You might well never envisage doing those things, but then again, you probably never envisaged buying a shotgun anyway. So it's future-proofing really. As for makes, you've probably heard of them anyway, but the usual suspects are Browning, Beretta, Lincoln, Webley & Scott, Lanber, Bettinsoli, amongst others. Obviously some of those come at more of a premium than others, but they will all throw an ounce or so of pellets along and out the barrels much the same.
Don't dismiss used guns either. You could get a better gun used for the price of a cheaper one new and it's easier to check how worn a gun is compared to a rifle. Just check the barrels are nice and shiny, it cocks and fires and ejects okay (if in a shop, obviously use snap caps and tell them first) and check the woodwork closely for any signs of cracks. If it looks too shiny, check even closer. A bit of wear, so long as it isn't much is no bad thing, probably just caused by handling by the previous owner over a year or three standing on a peg waiting for a bird to come his way. Take the fore end off and see whether you can wiggle the barrels and if they are a bit loose against the action, move on to the next one if they do. Shotguns, if not abused do tend to last pretty well usually. Hell, all those 19th century examples knocking about can't all be wrong.