Hi ! After a little work with Boost.asio here is what I can say about starting with it :
If you want to learn and practice low level networking :
You should use boost, which allow you to do basic networking stuff without care about the threads stuff. The tutorials and samples are really good to start and you'll be able to understand faster other libraries.
If you don't want to learn low level networking (You need to decode the header... the body...) and want to quickly setup your network :
Use raknet. You can find it on github here, and if you're an indie and your budget is less than 100K, raknet will stay free for you. You will be able to quickly make a chat with the RPC functions (that's magical !).