What sort of riding do you do? If you only ride motocross, I'd recommend a glide plate as it's lighter and doesn't collect as much mud. If you get a glide plate, go for a carbon fibre one over a plastic one. I primarily ride offroad (enduro, harescrambles, cross-country) so I need the full protection provided by a skid plate. The protection does help in motocross too as I don't have to worry about a rock punching a hole in my cases or clutch/ignition/waterpump covers. How much protection do you want?