Only read if you are bored

You guessed it, another what lens question. Looking for one more lens to compliment what I have now. My thoughts are the new Canon 35mm, the new Sigma 35mm or the the 135 which is what I have been lusting after ever since I had to decide between my 100 L and the 135. I would like a longer L zoom but that's not in the cards anytime soon. My photography is general and don't mind bringing all my lenses and using the one that fits the situation. I do like candids when shooting people.

I'm bored. I'll play. 135L is awesome if a little long. 35 1.4 is my lust for lens at the moment. I'd wait a little to see proper ff samples from the new Sigma 35 and importantly how the AF performs. If it's as good as it looks it might be then it'd be a toss up between these two for me. I have the 135L, even though the design is older than most, the IQ is right up there. Whichever you get, shoot it wide open and be prepared to be amazed.

tough choice between those. The 35L is a great lens which I had for a bit but for landscape and outdoor shooting I found that I wanted just a bit more width which led me to want the 24L II which i'm gonna pick up as soon as I free up some funds.
Now the 135L is to me my favorite lens next to the 85L II. Its a great lens for candids, has a nice weight to it and the Image Quality is just remarkable for an "L" lens at its price.
If you find yourself shooting more candids and people then I say go for the 135L.
But if you are into landscape and outdoor shooting then the 24L and 35L are a good choice.

Just gotta decide on what you know you will shoot the most then take it from there.

I should have been clearer on the 35mm. I meant the new canon 35mm IS that due out.

I'll play... only read below if you're bored

I have the same lenses that appear in OP's sig plus the 135L in question. I also rented 35L this past summer and when the time was up, it felt like giving away my favorite puppy or kitten. I'd assume 35IS's image quality should be up there on par with L lenses.

I've built my lens lineup so that the zooms are at f/4 (with the exception of 16-35, because I need that extra f stop for handheld interior shots), complemented by fast primes at key focal lengths.
Since you have the 100L in the tele range already, how about one of the 35mm choices to complement the 24-105. In fact, if I had to own just two lenses, it would probably be the 24-105 and a 35.

135L might be too long for candid shots, but that's just me. It really depends on your shooting style -- do you shoot outside of the action looking in or do you immerse yourself in with the action? I tend to be in the latter most of the time and hence one of the 35mm prime options (35L, 35IS or Sigma 35) is high on my next lens purchase.

100L and 135L are very different lenses but in a pinch, 100L can cover 135L's ground. 135L focuses faster, but if you apply the same trick 85L II shooters use, which is to manually focus close to the anticipated distance, the 100L will focus right away. Using distance limiter selection switch on the lens also helps. 100L's bokeh is not as creamy as 135L but the lens is plenty sharp enough.

I have the 135L on a crop sensor, and the lens is absolutely amazing; sharpness wide open, bokeh, colors, everything. With that being said, it's a little long on a crop. I see that you have an 5DII, and since I love the focal length of the 85mm on a crop, I imagine the 135L would be great on FF. I can't wait to get a FF camera just so I can really get the maximum out of my 135L.

Plus, used 135L's are being sold for pretty cheap right now. You can find one for $700-750, which is a very very solid price for a phenomenal lens.

The 135L is definitely my next lens purchase. Got to use one a few weekends ago and it was top notch. Bokeh was amazing and the subject was sharp even wide open.

If you are a diehard portrait person (candid or posed) go 135L. If not (since you have the 100L), decide what you want IS or f/1.4 and go for the 35mm. IMO the 35mm gives you something in FL and speed that you are missing more in your lens lineup compared to the 135mm.