Bargain silent movies can be a risk. I often prefer more "mastered" (and expensive) DVD versions if the print is in bad shape. But all three of these were very good to look at.
I am a fan of Douglas Fairbanks movies, and the Black Pirate is one of my favorites. My favorite scene is Fairbanks capturing a merchant ship with passengers aboard single handed, and without firing a shot. NOTE: If you are looking for a good quality print of the Black Pirate, there is now a release from Kino Video (available here on Amazon), that is absolutely amazing. The film was originally filmed using a very new two-color Technicolor process, and this new release lets you see the the full beauty of the red and blue Technicolor dating from the age of silent movies! It also has about two minutes of footage not in the version on this disk.
The Iron Mask is also good but Fairbanks' character is older and he doesn't reach his usual level of athleticism. I also find that the story has the feeling of a sequel and is less engaging because of that.
I have always been a fan of The Scarlet Pimpernel. I was not overly impressed by the lead in this film but it was still a very fun adventure/romance. If you have never read or seen any version of the Scarlet Pimpernel I recommend that you do so. This would be a very good place to start. (My favorite version is the recent A&E/BBC production starring Richard Grant, who manages to pull of the difficult task of playing a brilliant, swashbuckling, foppish idiot with more believability than those contradictions ought to allow.)