Kind of like deciding where to go out for dinner, only 1000 times more complex
I'm lucky, my wife is willing to follow me anywhere -- mutual, I assure you. It's hard to pick the best trips we've made together, whether it's caving in Borneo or cycle touring through Banff. (After each trip, I get an earful, though, on what I shoulda done different....)
Here's four things I've learned about team or group activities, applies to just about anything, not just touring.
-- If there's one person who's most accomplished and experienced, that person can usually make the decisions (the important ones -- route, schedule, difficulty, etc.). That person doesn't have to be a natural leader, but they have to be attuned to other people's needs and abilities. Most mature people in the group will accept this role, as long as the "leader" doesn't screw up. If you're that "leader", it's a very satisfying role to see the team succeed. Corollary: If a second person in the group is most experienced in choosing food/entertainment/whatever, let them take the lead there.
-- If you're not experienced and accomplished, join up with someone who is. Don't put all your trust in them until they prove themselves; don't let them do all the work (unless you've paid big $$$ for the privilege). Learn and share, but mostly learn because they're making the big decisions that determine the team's success.
-- If the group is equal in experience, go as an organized club. Pre-plan (within reason) the route, the difficulty; loosely pre-plan the schedule, the costs. I've been on group tours that wouldn't have worked as "hey, ya wanta go for a tour?", but were a blast as a club ride. Local bike clubs here have fantastic week-long self-supported tours, from 12 to 20 riders, open to anybody. Never had so much fun!
-- Riding solo is a soul-cleansing experience. There's nothing like knowing you can challenge anything nature throws at you and come out on top. You can do this once, twice, or all the time, choosing your own challenges. Only thing you don't get is the social interaction of learning and sharing how to overcome them.
In a group, any personality conflicts can destroy the first three scenarios. Choose the group carefully.... but still it can happen.
You might find #1 most satisfying -- try to find some friends who are adventurous enough to go, but need someone to take the lead and learn from. You still get to make the big choices, and cooperating on the little ones ties everybody together.