I would think about what you want to fly. Then I would think about whether you want to go on flying the same aircraft after the conversion while you gain some experience. Those two elements may be determining factors.
I might then think about what runways are available at the aircraft's home field. Shoreham and Goodwood have the advantage of six runways.
After all of that it boils down to what the instructor is like, aircraft availability and whether or not you will be able to rent the aircraft for self fly hire after your conversion and inevitably the cost - although I doubt this will varying significantly between clubs being more a factor of the type of aircraft.