1. Raiders
2. Last Crusade
3. Temple of Doom
4. Dial of Destiny
5. Kingdom of the Crystal Skull
Raiders is close to a perfect film. The entire thing just keeps moving forward with one classic scene after another, and almost no time wasted. There is basically nothing I would cut from it.
Last Crusade is a bit more stretched out, and I don't think really gets great until Sean Connery shows up. It is fantastic after he does though, and it has the most emotional stakes.
Temple of Doom is stupid and weird, but certainly an exciting adventure and never boring. I like how different it is from the others.
The other two both really suffer from Harrison Ford being so old and not being able to do what he used to. Of the two though, I enjoyed Dial of Destiny quite a bit more. The opening 20 minutes was like a movie of itself, the overall plot was more interesting, and the action scenes were by and large better than the ones in Crystal Skull.