Right now Heavy Dun Hunter. I usually look for the best combo of speed, maneuver, and charge. Armor is least important except vs knights or heavy infantry or mass archers but mass archers is usually bad idea solo unless they are really low level.
Well my PC is only level 8 so 20-30 D'Shar Raiders is still a challenge at that level. I think part of the problem is 5 riding on a 3 mount makes it go pretty fast and the D'Shar chieftain for some reason runs right for the map edge nearly every time. It is also sometimes just a bit too tempting to chase the guy down who I know only take one more hit to kill and get a little to close to the edge but it is hard to judge. I thought I read about a mod which painted a color on the ground at map edge which takes a bit from immersion but then so do invisible walls.
Usually I can notice the different textures on the edge but terrain with some small hills or trees even in the steppes can make it hard to spot. I actually never knew about the minimap. I always thought it was weird there was absolutely no reference point once on battle map. Been lost on there so many times.