In order of greatest to least. Excluding Indy of course.
Just an epic enemy. In my opinion Indy's ultimate rival. Belloq just had some of the greatest lines in ROTLA. He was also a break from the stereotype Nazi's that Indy always fights.
2: Henry Jones Sr.
Sean Connery, a great actor. He got some great lines in LC and provided some good laughs.
3: Short Round
I think Shorty was one of the best parts of TOD. Funny, loyal, and just a cute kid. It was nice to see Indy as a sort of a Father figure.