Only thing I would suggest (on having used three different brands myself) is that some will work with the (albeit primitive) built-in bluetooth functions of XP SP2, while others require thier own specific software installed to communicate with the device.
Better brands don't really mean better service. Range's are also not brand dependant, some are 10m (like most mobile phones) and others can be up and above 100m.
eBay is a glorious place for all things bluetooth and dongley (not a word, I know!). Just watch for the postage costs from Hong Kong!!