I am looking to buy a sd, sdl, etc... Money is not an object (i only want up to year 1991)

My question is...what is the best model/year to purchase..

I have heard to stay away form the 350sdl...orig my first choice as usually the newest models are the best ones...

That said, is the sdl different from the sd>? The engines are not the same?

What do you all reccommend as the most trouble free and most "choice" model

any and all suggestions woud be greatly appreciated...