Great Amazon discussion.
Two characteristics you may want to consider when purchasing a Bluetooth adaptor are its data transmission speed and its range.
The data transmission speed of a Bluetooth adaptor (a.k.a. dongle) depends on the adaptor's protocol version. The products that sell today are either Version 1.1, 1.2 or 2.0, with the last two being more dominant. Version 1.2 operates at speeds up to 0.7 Mb per second and Version 2.0 operates at speeds up to 2.1 Mbps (3x Version 1.2 speed).
Bluetooth adaptors also have a 'Class' rating which determines their range. Oldest (and now obsolete) class is 'Class 3' which had a range of 1 meter (~3.3ft). Today you can find products that are either 'Class 2' or 'Class 1'. Class 2 Bluetooth devices transmit up to a range of 10 meters (~33ft), while Class 1 devices transmit up to 100 meters (~330ft). Classes are not version specific; older Version 1.2 adaptors are Class 2, more recent 1.2 and 2.0 Versions are Class 1.
An important thing to keep in mind when buying a Bluetooth adaptor is that neither the connection speed nor the range of your network will fully be determined by your adaptor. After all, it's a network and the receiving device also has a thing to say (bottleneck issue). A Class 1 , Version 2.0 dongle, for example, will not perform up to its maximum range (330 ft) or maximum data transfer rate (2.1Mbps) if it is paired with a receiver device (headset, printer etc..), that is Class 2 and that is Version 1.2. The speed and range of such a network will be closer to the inferior values in each category, in this case closer to those of Version 1.2 and Class 2. However such a network should still work fine because the version and class protocols are backward compatible; units with newer protocols will work with units with older protocols.
To sum up, buying the adaptor with the best features will not necessarily make your Bluetooth network faster or further reaching unless it is paired with a receiver device that is equally advanced. Today, for example, almost all Bluetooth headsets you can find in the market are Class 2 (for practical power saving purposes, since these devices need regular charging) and hence will not work at distances much more than 33ft even if they are paired with Class 1 adaptors.