i suppose "best" is a relative term. You have to consider loads of factors, eg, if you are having radiotherapy every day, or regular chemo, do you want to be travelling 100's of miles whilst feeling like poo? What would happen if you wernt feeling well enough to go? can you afford the fares to get to these places? (you dont get any government help if the treatment is avavilable at your local hospital, but you chose to go elsewhere) If you had to be admitted because of side effects, would that be at your local hospital? How do you feel about having more than 1 consultant involved in your care?
research and clinical trials are going on all over the place, and everwhere uses the most up to date trials to inform their practice.
In essence, most people go to their nearest hospital for cancer treatment, and get referred to places like the marsden if a second opinion is sought, or if, for example, the lacal consultant dosent want to give any more treatment, but the patient requests it. they are more likely to do "last ditch" stuff, plus the phase 2 and 3 trials at a specialist centre