Thanks for all the advice. We have/are considering Knutsford. Our only hesitation is we tend to be the stop on the spur of the moment or when we see something interesting type of people. With the long drive that may not work well.
Knutsford shows about 5.5 hours driving on the website. I was under the impression that by car and using the south coast route it was a 3.5 hour trip. Is this accurate?
Stopping won't work - the Knutsford only makes scheduled stops.

When I took the Knutsford in April to Kingston I actually had a taxi drop me in Sav to get it, and the ride from there was only 3 hours (I see they now offer the south coast route to Kingston from Negril too so maybe 3.5-4?). The north coast route probably takes 5.5 (including a longish rest stop).

If you want to stop at will, get food, take pics, whatever, definitely take a private taxi.