Looking to buy a coach shotgun. Looking for advice if I should go with a single or double trigger?

For SASS shootinf I like the double trigger myself, so does my wife. Mindset sorta thing, not a real issue. You get used to it with practice either way. So go with what you prefer.
Which coach gun/ Did you get /or do an action job on it? That's  the real important issues with doubles in SASS shooting. Fast load/unload ease no double trigger/single trigger as far as times /speed go.

2 triggers are mechanically simpler........

I love the double....Alot of times I see guys that the first shot doesn't reset the single trigger for the second shot...You'll spot those guys that are banging on their butts. I use the 2 triggers and don't even think about it.

Obviously, a single trigger is potentially much faster.

But, as others have pointed out, the gun must be properly set up to realize this advantage.

I used to use a double trigger Stoeger.  It was a good gun.  I now use a highly tuned SKB –– in fact I have a number of them.  My match times went down by almost 30 seconds when I made the switch from the Stoeger to the SKB.  Not all of that time is due to the single trigger, but much of it is!

Get a good single trigger gun from a good CAS gunsmith.  Don't mess around with other solutions.  Believe me, doing it right will save you lots of time and money in the long run.

Remember, ALL OF THE TIME IS IN THE SHOTGUN.  That's where you want to spend your money.

My experience mirrors RugRat's.  I was fighting with my Stoeger for years until I happened to be on a posse with Johnny Meadows.  He said, "You've got about $1,000 worth of pistols strapped around your waist.  You've got about $1,000 worth of rifle sitting in your gun cart.  Why on Earth are you skimping on 1/3 of your arsenal???"  He then let me shoot a stage with his SKB and I never looked back.  The shotgun instantly went from my worst gun to my best.  And as far as single triggers not resetting, he's got a new mechanical reset single trigger that's as slick as can be and eliminates the problem if the old inertial unit not resetting.  Even Evil Roy traded in his Brownings for Johnny's SKBs.