I've just booked LGR-GVA for 20 students as a group. Price was £133 return per person for 20 seats and cheapest fare online at the time was only a little less (so to get 20 seats at that rate was great - it's been closer to £150-170 in previous years). No hassle with anything, really easy to add names and APIS etc, names only two weeks before. And low deposit of just £20 or £25 per person, can't remember exactly, which is useful while you wait for the kids to pay the balance of the trip.
We booked flight only and then a hostel in GVA.