Usually built with -O3, maximum optimization, the plain r3 version. People asked for other versions to test, the r3_O2 version is built with -O2, highly optimized but often safer (stabler) and the r3_s version is built with -Os, optimized for size, then speed, perhaps best on memory restrained systems.
As I said, they were sort of experimental as someone questioned my using -O3 so I built the others for comparison. The seamonkey-2.42.9esr_r3.en-US.os2.zip is probably the best.
As Dave knows, I was the one who was whining about over-optimization, so he obliged me with the several variants he mentioned above. Although I tried all 3 versions, I settled on the -O2 build because that's what I wanted in the first place.
I don't know if it was the choice of optimization or the fact that Dave built these with gcc 5.x rather than gcc 4.x, but this is the most stable version of any mozapp I've ever run. I installed it on June 6th and have yet to get a .TRP (crash) report in my SM directory. Of course, the thing still has many, many problems - but to go for 4 months without a crash is still extremely impressive. Thanks, Dave.