bovine valves seem to have a very slight edge according to studies, but the research is difficult due to different manufactures.
I'm not sure what you mean by a larger valve as opposed to a smaller one? The orifice size where the valve is placed determines the size, it isn't a choice as far as I'm aware. If you want a larger valve, you would have to restructure the top of the ventricle and this wouldn't be recommended.
Will a larger bovine aortic valve last longer than a smaller one?