Which boiler is best for 4 bed 3 bathroom house - Vaillant, Baxi or Worcester?

My first choice of manufacturer is Worcester Bosch, followed by Valliant, You will need a 'system boiler' NOT a combi. You have stated their are 3 bathrooms, therefore your domestic hot water demand will be high. Also have fitted a un-vented cylinder appropriately sized to suit your hot water needs, this item of equipment is a must to serve this many bathrooms where you will have simultaneous hot water demands. Your system boiler size also will have to be calculated by a heating engineer as this involves heat loss calculation. As for your choice of installer - British Gas, you are either a family member of Rothschild's or you are unaware that they never have nor ever will offer the customer value for money. Consider other Gas Safe engineers (sole traders) who are far more competitive than BG! Ps. Invite BG to quote first then others

i would go for the worcester high flow as this will be the only boiler capable of supplying hot water to all your bathrooms,but you will notice a drop in pressure on your hot and cold water anyway when any water is drawn from a tap. also you may need to upgrade your water main to keep up with the demand of water. british gas over charge and use contractors anyway so may as well get a sole trader in ,that will save some money also. some gas engineers will be able to offer you service plans and guarantees with certain boilers aswell .