In terms of the stuff that carries one of the major Shimano model names it's fairly straightforward which is the "best", or at least the "most expensive bought new." Some more obscure things like small-hand-sized shift levers only have model numbers. Less visible components like cassettes, chainrings, and bottom brackets also sometimes have numbers only.

Shimano road stuff (high to low):

Dura-Ace, Ultegra (formerly 600), 105, Tiagra, Sora

Shimano mountain stuff (high to low):

XTR, Deore XT, Deore LX, Deore, Acera, Altus, Tourney
Saint is downhill-specific and I gather it's XT-ish