Raiders is probably the best in terms of emotional impact. In that respect it's definitely better than Last Crusade and KOTCS, which spend a similar amount of time on character relationships but never make them feel quite as deep as Raiders. However, I definitely find Temple of Doom more rewatchable and a more ideal portrayal of the Indiana Jones character. The Temple of Doom Indy is the Indy we were introduced to in the opening of Raiders but we get him for the entire film this time...the aggressive, learned, fortune-hunting adventurer with a grizzled exterior and a heart of gold who escapes danger with equal helpings of wit, skill, brawn and just plain good luck. Indy throughout the rest of Raiders rarely feels like he's that iconic of a character. He feels more human and down-to-earth, which is the movie's strength I suppose, but also less symbolic as a heroic figure, which is Temple of Doom's strength.
In a way we see less and less of that heroic Indy in Crusade and KOTCS, where Indy becomes downright passive and reluctant in his adventuring and even turns into more of a comedic figure, bumbling and stumbling around (falling down the stairs in Crusade or the KOTCS quicksand scene for instance). So for me, Temple of Doom is the ultimate portrayal of Indiana Jones and probably does more to define the identity of the character as most people perceive him than even Raiders did. I wish Spielberg and Lucas hadn't apparently decided to more or less disown Temple of Doom, because the further sequels would have been well-served to stick closer to that portrayal of the character rather than seeming to make an almost conscious effort to be different from Temple of Doom. If nothing else, Temple of Doom with its lean, self-contained story and its centralized focus on Indiana Jones himself presents a much better model of what an Indiana Jones SEQUEL should be than does Raiders, which Crusade and Skull clearly tried to copy more directly from, generally not to great effect (those films worked best when the scenes weren't reminding you of Raiders). Temple of Doom presents a much sharper formula for building a sequel around whereas Raiders isn't a story you can effectively repeat without either seeming like a pale imitation or a watered-down version.