It all depends on the instructor and the information presented in the course. If they are just the basic outlines that most agencies present, I'd have to say none of them. If you get an instructor that presents additional valuable information, then they all have potential.
I'd say the ones that have the most potential are the following:
Enriched Air / Nitrox - It's just good information to know, even if you don't dive it much.
Wreck - It could be the beginning of running reels, shooting bags, horizontal orientation, different propulsion techniques.
Deep - It could be where proper gas management planning is learned.
Cavern - Definitely the best class hands down. Lots to learn if taught properly.
Ice - Special circumstances due to the environment. Has lots of potential.
U/W Photographer - Actually, the digital one could be great if a lot of classroom time is spent after the dives learning how to edit the photos.
U/W Navigator - when done in low visibility.
DPV - There are special techniques dealing with DPV failures.
Night - Communication, keeping track of each other, and just the introduction to the dark.