I think if you're the type of group that are fairly easy going in terms of what you do, then a guided tour is great because its fairly stress free. But if you guys have a specific list of things you all want to do then i'd consider brain storming an itinerary and maybe combining short tours + time to yourselves to do the things you want!
I'm personally not a fan of tours because I love making my own adventures and feel so great when I've turned down a random road/lane and bumped into the best bar or shopping centres!
Ultimately its up to the group! and remember to sometimes take time out and chill because sometimes you've felt like the holiday wasnt really break. I'm currently planning a group trip for my mates bucks and its pretty difficult keeping track of things. I did stumble on this site
www.troopr.com though, me and my mates have signed up and hope it will be ready before our big trip..
It's for groups to organise travel.