For Windows10 @ RPi2/3, this is not a normal Windows10 but a platform for services, which you have to implement in Visual Studio. There is not even a real graphical Interface.
Afaik there is no (or no easy) way to install Java or to get openHAB working @ windows10IoT.
Apart from that, RPi3 has a Quadcore 64bit ARMv8 Processor with 1.2GHz, should run nearly 50% faster than RPi2. It has as benefit WLAN and Bluetooth4.1 onboard (by-product of the used hardware I think) so this could be interesting as well. And Raspbian is imho a very suitable environment for services like openHAB.
Maybe the only downside is the lack of SATA or fast USB ports.
I guess the real question is… from what? RPi1, RPi2, something else?
From my understanding based on reading here RPi1 struggles a bit (but still works). Probably a good upgrade. RPi2 seems to handle fine. Maybe if you have another use for the RPi2 then it certainly won’t hurt. Personally, I’m not going out of my way to upgrade from a RPi2 to the RPi3.
Ok, RPI2 is working fine but sometimes struggles when running mopidy and openhab… So i thought Rpi3 might be a nice upgrade. Especially since I need a new RPI anyway:)
The reliance on SD cards for the raspberry pi has always made me nervous of running OpenHAB on them as I’d assume there would always be lots of read/writes.
I seed the Odroids also have eMMC storage which might be more reliable?
One note, the Pi 3 is a 64 bit ARM, and there are some problems with this architecture around the usage of serial ports. If you are not using any serial/USB devices with OpenHAB, it should be okay. Here is a link for more info: 64 bit ARM serial