I had exactly the same choice this spring. I decided to go with the Kubota, even though I have an excellent John Deere dealer just down the road. The deal breaker for me was the three range hydro on the Kubota vs. the two range on the Deere. I have over two acres that I mow, with a large hill. The JD will not mow hills in high gear. Search the site, and you will see several threads on this topic. The JD2305 has the same engine as the JD2320, but is geared differently. As a result, high can be used on the JD2305 when mowing on inclines. Because the JD2320's high gear has a much higher top speed than the JD2305, it is limited in terms of how much power it has to navigate inclines. If I were you, I would test drive the JD2320 on a hill in high to satisfy myself that I could live with this limitation. I couldn't given my circumstances.
The Deere has several excellent features that the Kubota doesn't have. It has position control, standard quick attach loader, better PTO engagement system, plus the split brakes on the left side (some like this, and some don't). The Kubota has a better operating platform (it is much larger and more comfortable than the JD2320), nicer loader stick and controls, better seat, no position control (just the quarter inching valve - which works very well for my purposes), plus the three range hydro. I mow my 20 degree hill in medium range which has a top speed of about 6.5 mph vs. the 4.5 mph of the JD2320 in low. This makes a big difference in terms of time when mowing a large area.
The JD does have a nice system for picking up the drive over mower deck after you've taken if off. I'm not sure why you would need it, since its a drive over deck - presumably, you would remove the deck in the location where you plan on storing it. Kubota's drive over deck is excellent, and is a breeze to put on and take off. I have had some issues with the height adjustment knob on my
B2620 - but my dealer is looking into this for me and I'm sure that this issue will be resolved.
The hydraulics on the JD2320 are very slow. You have to move up to the JD2520 in order to match the speed of the B's hydraulics.
If I did not have the hill to mow, I probably would have gone with the JD2320, as the dealer is close to home, and has an excellent reputation. However, I'm very happy with my
B2620, which was actually priced less than the JD2320, has loads more power, and is much more comfortable. It all comes down to which machine fits you best - good luck with your decision. Either way, you will have an excellent machine that you will enjoy and should last a very long time.