We had this choice and went for ensuite, on the basis that no-one was going to go to two flights of stairs for the loo so he only regular user of the ensuite would be the person who has the bedroom (ds15!). Also, when ds’s have left home and I Airbnb it to help pay off the mortgage, I might get more if it’s an ensuite
Ds moved into the loft bedroom with ensuite about 8 week’s ago and no-one else has used the bathroom up there to date..!
But... we’ve got a bathroom on the first floor and a downstairs loo, so we’re lucky there’s usually a choice. If we didn’t have the ground floor loo we might have gone for a separate bathroom (although an ensuite just sounds so lovely I probably wouldn’t have!).
Separate. Especially if there's another room up there. We have a toilet on each floor and they still are sometimes all in use, which would be inconvenient if there were someone in the loft bedroom (and MrNC works from home a lot there).
We have it separate as we'd come from a house with an en-suite & knew the disadvantages of that. If anyone uses it in the night, switching the light on or flushing doesn't disturb the other. Whoever buys the house next can very easily convert the bedroom into 2 double rooms & both will have access to the shower room. And it was a godsend when we had the main bathroom refurbished so everyone else could easily use it. It can also be used when we have a houseful so they're not all queueing for the other bathroom, without going in our bedroom.