which is best ? math honours or physics honours ?
If talking overall, no one is superior to other one. Both are equivalent. If somebody has interest particularly towards Physics and not in Mathematics then definitely Physics is best for him than Mathematics and vice versa. Bu if talk about future fields, then a Mathematics has more fields than Physics but it should not matter for a students who has interest in the field which is already available because other fields will not matter for such student.
Don't know much about Physics but physics has limited fields while Mathematics has broader scope i.e., A student opting for Mathematics can opt for being a Mathematician, Statistician, Analyst, Professor, etc.
Hope it helps.