30 feet and 9,000lbs (and upwards) is where it's at, for single-handers.
Smaller loads, less expensive to equip and maintain. Less expensive slips in marinas, and can squeeze into tight or semi-shallow anchorages depending on draft. Easier to dock, solo. Easier to DIY maintain.
I've sailed larger boats, and even with all of the lines led aft and set up for singlehanding, I felt that they would be a real handful if the weather ever got up. There is one large boat that I'd take on, solo...but I won't name her.
I'm a fairly solitary creature, so I rarely ever entertain more than 1-3 passengers. I have a head, a galley and music onboard, so I don't feel like I'm camping.
25 feet is too small. 35 feet would be my absolute max, and I probably wouldn't like it as much as 30. There are a slew of solid 30 foot, Good Old Boats out there:
I have a friend who's circumnavigated. He says that 30 years ago, people circumnavigated on 30 footers. Now, people will tell you that 30 feet isn't suitable to cross the Chesapeake Bay.