i always look for a maximum grip in the rear, using S-grips in the rear and M-grips on the front (we are only alowed Tamiya-tyres in our Tamiya-competition so I haven't got any other that I could try and compare).
Also I balance the car with some weight. Adding a bit of weight in the rear will make the car roll less forward when you lossen de the throthle when taking turns.
I prevent griprolls by giving the front tyres a small ring of CA-glue on the outer side of the rim. This makes the tyre just loosen some lateral grip, enough so that your chassis doesn't flip over.
(picture from RC-Tech, showing where to apply the CA-glue:
http://i94.photobucket.com/albums/l1...n_1985/red.jpg )