I know, it's hard to say what is better than what anymore with everyone putting their name on stuff made by whoever, wherever. When I was landscaping full time we used a lot of John Deere 48" walk behinds with sulkies and they ran 14hp Kawasakis that were practically unbreakable (and trust me they got worked very hard). But that was 20 years ago and I'm not sure if Kawasaki is putting that same level of quality into the motors they are selling to Cub Cadet, maybe, maybe not. Kohler motors are not as good as they used to be since they stopped making the cast iron work horses 15-20 years ago. They are OK but not worth the extra money they charge for them. I would rank the Kohler Courage as a lower quality engine, I'd rather have just about anything else but to be honest they are probably all about the same at that level. I'd take any Kawasaki over any Kohler any day and most Kawasakis over most Briggs and Strattons.
If you can get a Cub Cadet that you like and had the chance to try out with a Kawasaki motor than it's probably your best option in your price range, especially if you get it at a Cub dealer instead of the box store. I think some of the problems people have with box store mowers are from the poor assembly and setup. A dealer will at least assemble it and set it up properly (probably). Like I said, don't abuse it and maintain it faithfully and it should be good for you. Use a good synthetic oil and at least 90 octane gas to limit ethanol damage and keep the gas fresh. When you store it for the winter see if you can get some ethanol free gas with a good fuel stabilizer. If you can't get ethanol free gas use something to fight phase separation from the ethanol. I think Stabil Marine does that or you can use regular Stabil and Star Tron for the ethanol issue. Some people say the anti-ethanol additives are snake oil but I say they don't hurt and they cost very little for what you need for each gallon so why not throw some in there.
Oh, I looked at the wrong person, you are not in Cali, you are in VT. Anyway, I looked at used mowers too before I bought my new one and the good ones go so fast that it's hard to grab one, especially a month or so ago when mowing season was just getting started.