I’d say it’s very hard to generalise as there are so many variables, but 29ers will tend to be a bit better at ploughing through really rough stuff, and 27.5ers will be a touch more playful / fun if you’re a more active (body position wise) rider and/or on less severe trails.
But there are plenty of exceptions to this made up ‘rule’!
And of course there’s mullet options now (I’m confused why it’s called a mullet though, with the bigger wheel out front, surely it would be some kind of big fringed hair cut!)
If it feels good, ride it!