holdens is OKAY as long as you have a good exposing unit and washout area. holdens has destroyed a few screens of mine over the years, and to be honest, i dont even use the shit anymore. i spend the extra money to get good emulsion that i can trust.
206 is for oil based 250 is waterbased... or the other way around.
I've got a pretty ghetto rig and I use Ulano QTX (water-based pink stuff). I love it. Even though my exposing unit is made from Home Depot parts, QTX seems to work great for what I need, great detail. Burnt in 5 minutes with 2 "U" bulbs.