The best one was Sallah to me. With Henry Jones Senior possibly holding the second place... and "Mac" McHale being a very close third. That would be my podium.
Sallah is the essence of the sidekick itself. He is the best friend to Indy, and his greatest fellow adventurer. He is so human, so fallible. He is indeed the deepest sidekick character of the entire franchise. Not to mention he is also a really funny character to watch.
Henry Senior is legend, I know. There's no need to add any other words.
Then Mac... he was probably one of the very few redeeming things featured in the new film. After seeing the trailer I was expecting him to be some kind of coward "ball and chain" for Indy to carry on. Instead I was pleasantly surprised when I saw him so self-confident and courageous. Even when he was threatened to death by a legion of russian soldiers with machineguns, he was still inclined to his sarcastic british humour!!
And I loved Mac's empathy with Indy during the jungle chase. The way they temporary forget their rivalry and begin to fight together, and they kick ***es!!! One of the best moments in the film!!
And what about the grand-finale, with Mac sacrificing to let Indy escape? He is a loyal good guy, after all... and he is ready to face his responsibilities when he realizes his many mistakes.
No contest, Mac is GREAT!!!!!
Shame they decided to put Mutt in the movie so that there wasn't enough space left for him...