I haven't run into this "Best" adapter.

I've gone through 5 different bluetooth adapters. I use them mostly for my wireless headset. They have all worked relatively well most of the time, but I still haven't found an adapter that maintains a flawless and consistent connection, so I'd caution against expectations of perfection.

IOGear and Cirago both make a range of adapters that should be adequate.

This is really not enough information! We need to know on what you plan on using this for and what type. --(Keep in mind)-- Bluetooth, as of (Aprox) October 2011, Bluetooth standards were updated to *Bluetooth 4.0*. It allows for a higher data rate. the older style of bluetooth before Bluetooth 4.0 was based on its own technology, it was great, but it was known for a slow transfer speed. BT v4 is now closer to Wifi which made it much quicker, and it now is able to stream video!

I personally still have a Motorola Atrix 4G, which uses Bluetooth v2.1 (ANYTHING under bluetooth v2.1 With EDR CAN'T Stream audio)

On the other side, i have it connected to my Media Server and thus to my 5.1 Yamaha system. Plus, it connects my Logitech Bluetooth wireless keyboard for the media server.

The adapter i use is a v2.1 + EDR---> ASUS USB-BT211 Mini Bluetooth Dongle USB 2.0
http://www.newegg.com/Product/Product.aspx?Item=N82E16833320057

-TRM

Why did you have to encourage? He would've been fine with something simple. I originally asked if he was going to connect multiples or a single, but then I edited it out. I've had two threads that ended in very long explanations.

Why should I get 4.0?

Faster.
Multiple Devices
Increased Bandwidth.
Future Compatibility
New Class of Electronics

I imagine the only reason 2.1 hasn't been phased out is probably due to large volumes in stock.

I liked IOGears bluetooth keyboard (it can pair with 6 devices). It is tiny, though.

No one has mentioned that the adapters also come in classes such as class 1 = 100m range or class 2 = 30m range and there is a class 3 but its not really produced due to the fact it has a 1m range.

I do recommend getting a Class 1 adapter, it will still work with class 2 devices but you will have the extra range for class 1 devices, it all depends on what kind of range you need and if its available for brand and Bluetooth version.

Class 2 is 10 meters (30 feet). I do not believe Class 1 Bluetooth 4.0 adapters are all that available, yet.

There are Bluetooth 3.0 devices out with Class 1 range.

Class 1 adapters tend to be pretty expensive.

I picked up an Asus Class 2 v3.0 for $15 off of Newegg, works very well for file transfers to my handset as well as streaming audio to BT enabled amplifiers. On Vista/7/8 it operates pretty much driverless (embedded driver in the OS works fine).

I have a AZiO BTD-V201 Micro Bluetooth Adapter USB 2.0 and it works just fine with my Samsung phone to transfer pictures and stuff.