Mad Dok with Grots who have Cybork body. That's fearless, 5+ inv, Feel no Pain, BS4, 8 point meat shields! Plus you got Runtherders who take off an attack from the model you're atacking. Monstrous Creatures beware!
Although he's still probably better with Boyz.
grots don't get feel no pain vs s4 or higher (due to their toughness of 2) so I'd say always stick with boys or better.
I used him in a 1500 pnt game vs chaos marines a few weeks back. I just slapped him in a squad of 30 choppa boys and ran em accros the field, it took them 3 turns to get into combat and i had lost only 7 orks before the cc started without them having any grot screens or so. and then in cc they commenced to squash 1 squad of plague marines, 1 squad of normal chaos marines a squad of havocs and half a dp (warboss on bike did the other half

)
Now ofc this was just a one time use and a was fairly lucky with the rolls, but he made a fairly proppa impression on me, alto you do need to work with his one scalpel short rule and try to prevent him running after something that's in the completely opposite direction of where you want to go.
So i deployed his squad between the table edge and a big squad of shoota boys so he would have some trouble guiding the doc around without coming within the fire range of them.
edit: i can't type.....