Players should be able to adapt to any well-conceived system, while the GM needs to be completely comfortable with the system he's running.
You really have to consider the idea that every body at the table is part of the game. As the GM you have to be enjoying what you are running so the game choice is important to you. As players in the game if its not the game you wanted to play why are you there.
So my best bet is when I start to look for a group to GM for I let everyone know what games I like to run and let the players have input as a group forms as to what genre they prefer to play in. Once you have this locked to a majority rule usually every one is likely to be happy with the end result.
If you have a preformed group you generally know whatís going to fly with your players. But spice is the life of gaming, I like to try new systems and play around with different genre. This sometimes becomes something you have to sell to your players.
Above all as a GM try to learn to be flexible mastering isnít about being ďThe MasterĒ itís about be a master of the art.
Since I'm the GM I pick the system. Of course the system I pick is going to be Hero System, so I can run any type of genre the players decide to try. My old playtest group started with a western until they were comfortable with Hero then I moved them to Inceptum Terminus. They had a blast creating characters for both genres.
I've always had the DM choose the system, and that's most often been me, so mostly I choose.
Right now, I'm starting a group (our first meeting is this week) and I told them all that we'd be playing D&D3.5, though I'm letting them choose, or at least have input, in the world and focus of the campaign.
Parentheses are (not) important.