If you want a .28 the GRP is probably a good choice, I haven't driven one but I heard it's very smooth unlike most other .28's
If you want a .21, I use a Novarossi 21-5K - it's perfect for a truggy in my opinion. A RB C6 is probably another good choice. I currently run the Orion Wasp in my buggy, it seems to have plenty of power as well.
You'll need a servo with a lot of torque for the truggy, When I had the CRT I used a JR 9000T, plenty of torque and pretty quick too.
I personally like Hitec servos, something with 300 oz or more of Torque is great for a Truggy