All the Canon lenses are fantastic, but I'd say you have the best one. Speedy, sharp, contrasty, the 1.4 is a killer lens, but each you listed is radically different. The 1.8 is extremely sharp. The person above must have a messed with one. The 1.8 is as good as any Leica lens, for sharpness and contrast. The 1.5 is a Sonnar, I've tested it a lot compared to Nikkors and Jupiters. It's a very, very good lens. It's look is classic sonnar, very different from the 1.8 and 1.4. The speed lens, F1.2, can flare quite a bit, and is pretty soft.
Here is a test I did of the 1.2, 1.5, 1.8 a while ago: