Here's the first thing I would say against the 135, although I'm sure it's a heckuva lens the problem with all-around/general purpose may be the lack of zoom, it's going to rely on you to be the right area to frame the shot, so although you can zoom with your feet, you may miss a good moment being too close or far away. A good zoom in the same range would be the 24-105 F/4L, I've heard the 24-70 is amazing but it's more than twice expensive. Hope this helps, best of luck with your decision!
Ya I would look at the 24-105mm for an all-around lens. Anything with a wide zoom range will be all around. For a cheaper variant (aka more affordable) try looking at the 28-13mm, similar zoom range and more affordable. Of course the L lens is nice but it's not required because the 60D is a cropped sensor. Some food for thought and a cheaper alternative.
Grain is more caused by the sensor rather than the lens. It IS a bit softer wide open, but still very usable, and by stopping 2/3s of a stop it catches up to the Canon. If you plan on shooting wide open at 2.8, and print big, I'd save up and get the Canon (or wait and see how the new Tamron is going to fare up when it's released in December), otherwise, get the Sigma.
A 135mm F2.0 is not an "all around" lens, it is a very specialized portrait lens used for getting tight shots with super shallow depth of field. An example of a good quality "all around" lens in a similar price range would be the 24-105mm F4 (about $1100) or the 18-200mm F3.5-5.6 (about $600)
That is very helpful... I need a little help as a noob. I saw the 135mm on Digital RevTV and I loved the sharpness and depth of field - [link] But seeing you said it's not an all-round lens I'll go look into the other two you suggested. Thanks again.
Oh for sure, it is an amazing lens, no question about it. It just has very little versatility. It is a weird focal length that is too long for more scenic shots but too short for sports or wildlife. It is perfect for head-shots and portraiture though. Really if you truly want something that is versatile enough for shooting wildlife effectively you might have to look into a 70-200mm lens ($1350 for F4 and $2100 for F2.8)