I am a confirmed double shooter and 20 ga lover. Freely admitted. I shoot both SXS and O/U. Long barrel tightly choked (good as far out as I'm gonna shoot-won't say how far, but a LONG way!). Close barrel either open cylinder, skeet, or imp cyl depending on what the gun wants. These setups evolved after missing a couple of birds up close. I changed to the double and havent looked back. I shoot TSS 9s long range and Hevi 9's close. My family and I killed 9 birds last yr with these handloads. Closest 5 yds, furthest 46. The hevi 9's killed bird at 25 yds (not me and misjudged distance) DRT. Only two birds killed with long barrels.
Only two probs w/ doubles IMO. Unless you are willing to switch to a 20, 12's are heavy. Number 2, you are essentially packing 2 single barrels. If you miss up close, OK follow up shot. If you miss far, Oh well, NO followup shot. OK, I guess there is a third issue-you have to have the discipline to choose chokes and estimate ranges under fire-but DAMN it sure is fun!
Best Wishes.
Doc