Active Captain is worthless now that Garmin took it over. There is no fuel list anymore. You can get to see the marines that sell fuel by clicking on SHOW FILTERS than check gas or diesel. Doing this will show only the mariners that sell fuel and block out all the others.
The advantage they and Waterway Guide have over AC is that they proactively call fuel docks on a regular basis, so you are not dependent on someone visiting.
Active Captain is just about useless now that they have taken the routing feature out. I used to use it to figure distances between supporting marinas.
Cruisers Net and Waterway Guide are both excellent resources and both cover a very small portion of the world of boating. If you're boating in their area, great. Otherwise, they don't help you.