i will say i think the john deere deck seems to really perform well. i have never mowed with one though, but have years and 1000s of hrs on kubotas.
they will not let you down, and really have a great cut, but it does not do the best in very wet conditions as it is heavy, and remember we are using diesels though.
the deck will clog up in wet conditions while the jd will really not be affected that much.
you would not be wrong on either, but choose the things that are the most important for you .
right now while not in very heavy growth our kubotas are mowing fatastic and fast