There is no such thing as which version should I learn. It really depends.
First off all lets take versions 1.1 for example. It contains more than just rendering method. It also contains some other methods which are like a must for your application. So even if you're making a game with higher versions, you will need to use lower versions.
You should be asking what rendering method you want to use. There are few rendering methods available, however only 1 is supported by modern OpenGL. All the rest are deprecated. Here are the modes: (I might not even know all of them)
-Immediate mode - very slow, but very easy to use.
-Display Lists - very fast, easy to use, but cannot modify the data after you send it to GPU.
-Vertex Arrays - I think it is like display lists, but you can modify the data after sending it to GPU. It is easy to use.
-Vertex Buffer Objects (VBOs) - not the fastest, hard to use(for beginners), can modify the data. I don't really know the difference between VBO and Vertex Array, but I think VBO is better. This is the only rendering mode that is supported by modern OpenGL.
If you're just starting out in OpenGL, you should just go with Immediate rendering mode, which is all contained in OpenGL version 1.1
Hope this helps !
Check out some of these youtubers, they make pretty awesome LWJGL tutorials for beginners!
-thecodinguniverse - http://www.youtube.com/user/thebennybox
-thebennybox - http://www.youtube.com/user/TheCodingUniverse