Where do you want to go? If you are going in a group you need to consider everyone's wants and desires. Are you going to just Italy, just Greece or Iberian peninsula or the entire European continent.
What "style" of travel do you want to experience? This is where you must be honest wit your preferences and again your budget. Are you into relaxing stays or quick city in-and-out touring. Do you want to see a variety of cultures or do you enjoy one in particular? Do you enjoy indulging in hotel comforts or would you be comfortable in a dorm-style hostel.