You will find that there is a wide range of combi boilers from which to choose, and the one you go for will to some extent be decided by the size of your house, and the hot water demand that the boiler will have to cope with. Hot water demand is of more concern when choosing a combi - almost any decent model will easily cope with 7 radiators on the heating side.
Leading makes are:- Vaillant, Worcester Bosch, Potterton and Baxi.
My personal choice would be either a Vaillant Ecotech Plus or a Worcester Bosch Greenstar. If you have two bathrooms, go for the Greenstar 42CDi