That's not a simple question to answer. First, UPB is not HAI proprietary. UPB was developed by PCS and is a standard protocol used by several manufacturers. UPB devices are programmed via a freely available program called UpStart. Now HAI does have something called HLC which lets you program and control UPB without the need for UpStart. It works well for your basic stuff but when you get advanced you will need UpStart anyway. UPB is powerline based meaning all control signals are sent over your powerline. For some people with 'dirty' lines this causes a problem. Ra2 is a proprietary RF (wireless) system and can work without your powerline. Of course it is subject to other RF interference but it is pretty robust.
The bottom line is HAI supports both so the decision really comes down to other factors - you want to minimize RF in house, noise on powerlnes, look, cost, feel, breadth of device available, support, etc. Those are all things you need to consider before choosing a lighting technology. With Ra2 I believe the software is only generally available to dealers/installers and not the general public so that may be a small factor to consider.
Lastly, if you search these forums, especially the Home Automation forum you will find a plethora of information about lighting including these technologies (more so for UPB since it is more popular/widely used). User Neurorad knows alot about Ra2. And not to confuse but keep in mind there are other options like Zigbee, either like Centralite Jetstream or now any Zigbee that supports the HA profile.
Oh, and make sure your electrician puts a neutral wire in EVERY switch box!