This is so much a matter of individual taste and personal preference that it's difficult to recommend one above the other. Automatic or manual transmission? Both will get you to your destination, but they speak differently for you as a driver, assuming you drive both well.
Pump or S/S? You could say it's one of the choices that makes a statement as a shotgunner. Ultimately, it's what performs well for you.

I prefer a shotgun with a single sighting plane. I have always had a difficult time shooting side by side shotguns. You would really have to take the time handle and get familiar with all styles before you make a decision. The way that a shotgun points and comes to your shoulder is very important, that is to say the fit of the gun.

I'd base my choice on the situation too. If I am going to carry the weapon all day, I'll take the pump gun to save weight. If I need long range such as for goose hunting, the double barrels would win out. A pump gun with a variable choke or interchangeable barrels is also quite versitile along with being reliable. If I only could have one shotgun, I'd keep my Ithaca model 37 12 gauge. I have 4 barrels, including a slug barrel with rifle sights. Started out as a gift from my Dad and I added the extra barrels because I could afford them rather than a different complete gun.

A whole lot of what libertyfirst said.
I cut my teeth on a L.C. Smith s/s 16ga. Once I was informed that the barrels were regulated to shoot the same point of impact at 35 yards, my skills picked up a bit. Something you don't have to take into consideration when shooting a weapon with a single barrel.

Bubba

I like my 870. I can shoot it just as fast as my friend's autoloader.

Joe Kidd...How many gunners today do you think carry a SxS into the duck blind with them? I would guess less than 1% of the shooters.

I love pumps, thats what I would go with.

I have both and have taken plenty of game with both. A side by side has a certain class about it. My 870 wingmaster functions flawlessly in any weather. It is truly a matter of taste. Shoot scatterguns long enough and you will probably aquire a couple of each.

i love the look and feels of sxs and o/u, but i also like having multiple shots, and you cant forget that amazing sound when you pump an 870

To Sayfu: You're probably close with your 1% estimate of how many hunters in duck blinds are using a side by side. The guns cost much more than a capable pump gun. Not many firearms are abused as much as a duck hunter's piece.

pump for sure.

The pump is gonna be lighter and hold more rounds unless ur filming a western movie go with the pump.