Definitely look for something with a comb that's parallel to the bore; your cheekbone will thank you.
Also, just for the record, I will agree choke tubes make a gun slightly more versatile. However stock design and fit, in my experience, plays a far bigger role in the amount of success one will have as it determines where the pattern is going in relation to your eye. Imagine shooting a sporting clays rabbit with a high-shooting trap gun vs a flat shooting sporting clays gun. A bigger pattern might help you break the rabbit with a trap gun, but you'll be hitting on the fringe. I'd rather have the wrong size pattern going in the right place rather than the right size pattern going in the wrong place. And when it comes to spending hundreds more for a used gun with choke tubes, I'd rather just save the coin and get it threaded later.
So my advice (and it's really just free advice doled out over the 'net, so take it at it's worth!) is to buy a gun that fits, first and foremost; preferably with adjustable hardware for fine-tuning the fit and getting the best POI for the game you're shooting. Until you shoot a fair amount, your gun mount will very likely remain somewhat inconsistent, and having adjustable hardware will allow you to maintain a good fit with the gun as you refine your mount. Within a few months/years (depending on how much you shoot), you'll probably start really appreciating the nuances of gun balance, varying rib widths and designs, trigger pulls and lock time, bead styles, and all the other stuff that keeps shotgun makers in business. Subsequently, you may arrive at the conclusion that you like the way another gun handles better than what you're currently shooting... so just make sure that you invest in something that'll get you by for now, prove itself reliable, and will hold it's value or even increase as time goes by (be it through restoration work or gunsmithing such as having the barrels threaded for choke tubes), because there's certainly no guarantees that what you love shooting, and what you love shooting at today will still be your favourite shotgun, nor target presentation, in a year's time.