I have done two of them and doing one now. It was and is alot easier for me to pull the motor out of the truck and do it. I have a roll around stand built to hold the motor and I sit beside it and just do-it.
Depends on how mechanically inclined you are. Pulling the engine just makes it easier to get to everything, while keeping the engine in the truck you have to work against the firewall and anything else you don't remove in the engine bay. Seems like guys that do it often pull the engine, but guys that only do it 1 or 2 times leave it in. It's really a preference more than right or wrong.