Hello,
I use
JPSS for light shirts, which took me some time to get used to. Now I love it. I use Alpha Gold Dark for colored shirts, with OK results. I don't like the rapid deterioration of the opaque papers though, so I use light shirts almost exclusively now. My designs look best on bright colors, but I'm just not comfortable putting my name on shirts that won't look good in a few washings.
I don't sell any transfers. What kind of designs are you looking for? Someone else may have some, and there are places in the preferred vendors list at the left of the screen that sell all different kinds. You'll find something to your liking, and the prices mostly seem reasonable.
Good luck. It's a fun hobby/business to be involved in.
Paintergirl