First, see what rules they are using. If its an IDPA Defensive Multi Gun match, there are a number of equipment restictions on shotguns
IMO, the less "bling" on a competiton shotgun the better. A plain Mossberg 500, Remington 870, Winchester 1300, or Benelli Nova with a 22-24" vent ribbed barrel with changeable chokes will make a very good competition/ self defense shotgun.
My two competition pump guns are a Remington 870 with a 21" vent ribbed Rem Choked barrel and a Benelli Nova with a 24" vent ribbed Mobil choked barrel. I added a 4 shot extensions and opened and smoothed the load ports to make it easier to reload on the clock.
Also, a cylinder bore is worthless for knocking down plates or poppers with birdshot beyond 10 yards. I feel for the guys that bring their tacticool shotguns to a match only to time out or run out of ammo because their gun has no choke and wont budge a pepper popper at 15 yds.