For economy and 30, maybe 35 yard range then the Primos JellyHead in .570 constriction along with Remington Hevi13 shells in size 6 shot.
If you were asking for the ultimate, and price was not a concern, then either the IndianCreek tube mentioned above, or a PureGold .555 choke tube in combination with the Nitro Company's H276 Hevishot in straight 7's would no doubt be at the top of the 20 gauge performance heap.
Here's a pic of last weeks target, using a 20 gauge Express, Nitro H276 3inch straight 7's. 40 yards with the rangefinder. 217 hits in a 10 inch circle, using the Pure Gold .555 choke tube.