Sorry rccarracer- The GM is the only one I haven't owned so I can't comment! I like the Turbo and Protrak for different reasons but I currently have a Protrak!
The Indi discharge boards are usually copies of the Trinty boards, but cheaper in price!
The RT2 will discharge cells indivdually so you don't have to worry about going negative. If you leave the cells in the RT2 (and probably Indi) they will go down to around 0.02v per cell after about 15 minutes (after the lights have gone out). I would recommend the RT2 for equalising the cells before charging. The GM/Turbo etc are good for cycling cells and taking measurements of the packs performance (they're not bad chargers too!!