From my own experience, first choice would be a new Edrig, second might be any of the other Accucraft generics (new or used, but John has it exactly right, try before you buy). Side versus saddle tank? I've installed R/C in both an Edrig and an Excelsior, and found it a bit easier to fit all the bits in the side tanks. The new Leader (son of Excelsior?) is supposed to be more R/C friendly, tho, so maybe it's worth waiting a few more months for...
I did recently purchase a slightly used Roundhouse Millie, also another good choice, either as first loco or (as for me) backup to a larger engine.