I've been around lots of mowers and small tractors, but if someone said to me "grab a mower and drive it across the country" I'd get on something with a diesel Yanmar (Like dad's older Deere ZTR) or a liquid cooled Kawasaki. I know that's a stupid scenario, but darnit if those engines aren't freaking spectacular. The Kohler in my Craftsman is ok, better than a lot of other options, but it just seems so much "rougher" than the one in my JD.
We had a Dixie Chopper with a 26HP Yanmar (pretty sure it was anyway) and that thing was a spectacular POS. Leaked oil from just about every seam and bogged down and overheated when cutting tall grass. I'd take the 31HP Kawi FX850V on my mower over that diesel any day. It makes ridiculous amounts of torque has never had a mechanical hiccup.