i dont think there really is a "best" motor screw.. i regularly use whatever m3 screw i have sitting and it works just fine. but if I had to choose these would be my pick.
i stripped a thread on my vxl motor with those lunsford screws. i think it was my fault though. the washers aren't all that great in the lunsford kit. my motor still moved around quite a lot. i have better experience with the cheapo washers i got from taking my old busted weed eater apart lol.
They say a good mechanic only needs 2 tools - WD40 & Duct tape. If it moves, and its not supposed to, duct tape. If it doesn't move, and its supposed to, WD40.