There's no black and white answer here as DArt alludes to; it really does depend upon a number of variables and personal preferences. I won't vote for a "best" as it really does depend.
For the Gothics, Risens, Dark Souls and its particular related sub-type of action rpg with a heavy melee emphasis, third person is the best suited perspective no question for me. I like to see the Nameless Hero and be in better control of his actions as well as have greater awareness of what is happening, where enemies are etc.
For Elder Scrolls games on the other hand, I've only ever played in first person, as I've never found Bethesda's implementation of third person perspective to be strong or smooth enough to warrant changing from first person. I also think in their brand of games where the environments play such a large factor in immersion, that it's the most well suited view to experience their worlds.
Immersively atmospheric and highly interactive dungeon crawlers like Ultima Underworld and Arx Fatalis also truly went out of their way to make the first person perspective all encompassing, so much so that the player feels like that they're almost there. (Arx even has a key to eliminate the HUD entirely)
Thus, I doubt they would have quite the same impact if they were done in third person.