Accucraft recommends a variety of lubricants. The choice of lubricant is dependent on the parts being lubricated. Beyond this, it seems to me that choosing the right lubricant would also depend on the environment the engine is being run in. That is, heavy oils or light grease may be contraindicated when running outside where wind and dust is prevalent. In that case, perhaps the less sticky properties of graphite would be a better choice.
3 in 1 oil was my choice for servicing American Flyer locomotives. it worked well on the drive rods and valve gear. 3 in 1 even worked in the smoke generator. However, my parents were not impressed, they focused more on some silly oil stains on the living room carpet. I was five.
************************************EDIT***********************************
My mistake, I thought this forum thread was in electric powered models.