I've been involved in leading church groups for about fifteen years. Whether you lead a Sunday School class, community group, or men's study... finding the right study for your group is always a challenge. You want to find a study that is appealing to your group (so that people show up!), that has the right amount of prep work to fit your group's commitment level (again... so that people show up!), and of course, one that is spiritually significant (so that people actually GROW up!).
Personally, I am not a big fan of "taking a poll" to discuss what the group should study. I find that this can backfire and people start debating what study to the point that you cannot pick something without people being upset. Also, I heard a great tip one time that basically went like this: "The shepherd does not ask the sheep where they want to go to pasture." If you are the leader, then God has entrusted you with the responsibility of helping guide the spiritual growth of your group. Get suggestions if you'd like, but then pray and try to determine what you think God wants your group to be learning.
My last tip... is to purposely choose variety in the type of studies that you do over time. God designs us differently and no study is going to engage everyone. By varying the studies each time, you can minister to everybody. So one time, choose an in-depth Bible study that requires a lot of prep.... then read a popular Christian topical book on something like marriage... and follow that with a Christian Life DVD series, etc.
If you're interested in some recommendations, check out my reviews of 3 Great Small Group Studies that I've used with my church groups!