Technically, you remain the most flexible with an external IR receiver. And due to the lower technical complexity, IR remotes usually also give you much better battery life (turning on and off an IR diode upon a button press - vs - keeping an encrypted connection with a complex protocol open and alive).

The advantage of Bluetooth is that you don’t need an extra receiver. It also doesn’t require a line of sight. However, you should be aware that the OS X Bluetooth stack has been having issues with handling some of the Bluetooth remotes supported by Remote Buddy since Apple added support for Bluetooth 4.0 in OS X 10.7. I do think Apple will eventually arrive at a version of the OS X Bluetooth stack that’s as stable as it has been in OS X 10.6. However, until then, you can never know whether or not your remote, keyboard or mouse will still perform fine with the next release - minor or major - of OS X.

As for supported Bluetooth remotes, the only devices you should consider are the Sony BD Remote and the Wii Remote („basic“ version, the Wii Remote Plus is not supported as of this writing!). Support for Sony Ericcson phones has always been experimental and is more of an anecdote at that point. It will most likely be dropped in a future release.

Another option you have, btw, is using a supported RF remote. The Keyspan RF Remote for Front Row is now longer made as far as I’m aware of, but it’s a solid piece of hardware that works well with Remote Buddy. Chances are you can find a good price for one of these on eBay, too.

Which option is the right one for you is not upon me to decide though. It really depends on your individual needs.

Regarding the IR Receiver you bought on eBay: what are its USB Product and Vendor ID (you can find that info in System Profiler > USB or System Information > USB)? If you provide me with the info, I can try to find out more about it.

Best regards, 
Felix Schwarz