29” or 27.5+” on a hardtail?

I’m looking to get a new mountain bike in the next few months and have been struggling with which would be better for me. I will probably be riding mostly on bike paths and pretty smooth easy trails with my little guy, but I would also like something that I can be a little more aggressive on if I want to. I have been looking at the Giant fathom 2 and it comes in both sizes. I was hoping that someone on here would have experience with both and I could get some direction. Thanks!

Some frames are able to handle both tire sizes, e. g. Open’s One+. Of course, you’d need two wheelsets then.