Have using a few programs here is my thoughts.
STAAD is great, but to me the hardest to learn and utilize. It is very powerful, but not as user friendly. In my opinion, STAAD is best learned from people that use it everyday, and not through tutorials or manuals.
RISA is probably the easiest to use, and would recommend it if you did not want to do very complex structures, or did not want to integrate it as RAM Advanse.
RAM Advanse I feel is in the middle; it is more user friendly than STAAD, but not as much as RISA. That said it is pretty easy to maneuver and get good numbers. RAM customer service is by far the best I have seen out of any programs I have used. It is also good because it can integrate with Structural Systems (which I really like).
So, for a simple stand alone program I would use RISA, but if you want to integrate it later with a bigger system and need good customer service to help you figure out the programs I would use RAM Advanse.