matter of opinion
A topic that is subject to one's preferences. I know it's a matter of opinion, but I think that living in the city is more enjoyable than living in the suburbs.
matter of opinion, a
A question on which people hold different views, as in I rather like that design, but really, it's a matter of opinion, or The quality of that new stock issue is a matter of opinion. This expression was first recorded in 1843.