I've had the same experiences with all networks on trains, but for what it's worth, 3's mobile broadband is by far the worst in terms of both coverage and speed

I've had the same experiences with all networks on trains, but for what it's worth, 3's mobile broadband is by far the worst in terms of both coverage and speed (from personal experience and that of numerous friends). I'm with vodafone now and they're great (trains excluded).