Gerber Avalanche,Mansfield Summit or Kohler Cimmaron. I sell all three and they all flush great. I have 2 Gerbers's and 1 Mansfield in my house. My closet auger is rusting away in my garage.
Since you state you sell them, I have a toilet question. We have problems with our oldest who always clogs the toilet. I put the toilet in 14 years ago when I bought the house and had no idea what I was doing with a house.
So, looking at toilets now, I see 12 and 10 inch rough ins. My bolts measure 11 inches to the wall. The toilet is really tight up against the wall. Now I'm thinking I have a 12 inch rough-in toilet forced into a 10 inch rough-in. Does that make sense? I think maybe the wax ring is forced off a bit and "stuff" is getting hung up at the toilet/drain transition.
The story of replacing the toilet back then is I had it pulled up and the tank and bowl separated putting a new floor down. I was bolting it all back together at 8:30 at night with my wife 8.5 months pregnant begging me to hurry, lol. With only 1 bathroom, you don't leave an 8.5 month pregnant wife without a toilet very long.
I hear a crack and the bowl falls apart in 2 pieces. I look up at my wife wide eyed, "when does Lowes close?" It's 8:30 and Lowes closes at 9 and we're 45 minutes away. Needless to say, I was glad there wasn't any cops about. Took me 20 minutes to drive 40 miles to Lowes. Got back, toilet installed, wife used it, and 2 weeks later the one who clogs it every single time was born.