My first favorite lens was my 135mm.

I got the 70-200mm f/2.8 lens and it is my new favorite though. I just love the creamy bokeh that it gives. The compression is just gorgeous! It is heavy but truly worth it as you can get gorgeous non-distracting backgrounds anywhere! The best compression on it is when it is zoomed out to 200mm though so you do have to be a good distance away from your subject and it feels weird at first if you are used to using a 50mm lens.