We have opted for Thomas Cook over Thompson and First Choice on a couple of holidays in the last two years, One to Fuerteventura and the other to Ibiza both in school hols.
Both deals were for exactly the same accommodation etc and the price difference was huge.
Also would agree about the plane tho, TC seem to cram more seats onto there planes . This would put me off a long haul Holiday with them.

4 hours is a struggle packed in like that let alone a trip across the atlantic.