I've just dropped back to KS3.1 and WB3.0, after using 3.9 for the nearly 5 years (I think it was 2001 when i got it). My old 3.0+goodies set-up was much nicer, especially when used on TV (like I have to now due to lack of space).
Why WB 3.0? Why not 3.1?
I dropped back to WB3.1 after using WB3.9 for 2 months. I also had a much better setup than 3.9 and when I tried to reproduce my 3.1 setup in 3.9, I found that I couldn't.
The main problem was the stupid 3.9 picture.datatype. It always tries to remap and dither images that are already perfectly mapped - making image display 3X slower than the 3.1 picture.datatype and making all my WB images look like crap. There's no way to tell it "do not remap and dither images". I think the options are the lamely labelled "Best, Good, and Worst". (Worst still dithers and remaps!)
Maybe the 3.9 picture.datatype is great if you've got a graphics card, but if you've got an ECS Amiga, don't get WB3.9. Other ECS problems - no colourwheel for palette, annoying 256-step palette sliders - painful for ECS (what's 16x9 again?)...
Oh, and I think the 3.9 icon editor is total garbage. It is unbelievably badly made. It is extremely slow and jerky, painful to use, missing basic tools, remaps incorrectly and crashed on me many times. (the problem: is there another icon editor for colouricons?)
Now that I think of it (painful memories coming back), I think I was most digusted about what was NOT in 3.9. There were about 50 things that bothered me in 3.1 and I fixed them with excellent stuff from Aminet. When I got 3.9, I had expected that at least some of the major ones would be fixed. Instead, they just added some of the Aminet stuff I already had, other Aminet stuff that was worse than what I already had and left some of the major ones unfixed. Then they added more bugs and other things that needed fixing (by other programmers of Aminet stuff).
Well, I ended up stripping out the one or two useful things (like scsi.device 43.35) and using them in 3.1 and said "Hasta la vista" to 3.9. (...except when checking correct Cylinder counts on new harddrives ;-))