RCS - best fit and good quality, no problems there, well unless you run a vivid rear
Obtanium - made to fit every shock but to me thats a negative. unless your using a vivid you have to use spacers, also the same coil will fit 2.5 - 3.0 sizes. 3.0 takes another spacer though. so the only way it would be the perfect fit is if you had a 2.75 stroke vivid.
progressive - light, simple, but i don't think they make them anymore. i run a 425 on my intense SS which is awesome cause not many companies make shocks in increments of 25#
Diverse - newer company but cheapest. worth checking out.
Manitou and marzocchi - good quality as well. hard to find but they are out there.
i currently run a progressive and a RCS. in my experience a titanium coil is a titanium coil. progressive and rcs seem to be lighter when i have weighed mine though. I have ridden all but the marzocchi and obtanium.