Which lens has brought you the most...?

70-200L IS

Mine would be my Sigma 30/1.4. Though now I am toying with the idea of getting either 50/1.4. Or 50/1.2...:p

My 35L.

The 5D and 35L are a match made in heaven.

I don't have fancy L's 50mm mk I makes me happy every time

I'd say my 50mm. I'm doing a photo diary for my wife during a life event and I've used it for portraits of her and many of the visitors she has received. It's bringing both of us much joy during trying times.

Hmm, either my 135mm f/2L or my 300mm f/4L IS... Currently I'm using the 135L more

17-85 - so good I won't sell it.
10-22 - so good, that I'm MAD I sold it!
24-105 - not for sale! DON'T ASK!! Pry it from my cold dead hands!

100-400, My favorite!

10-22 / 100-400

17-40L

The lens I am the happiest with is my Canon 100mm f/2.8 macro. However I am happy with all my glass

70-200 2.8 IS has been my real money maker. But then I take advantage of what i use and buy only what I need, so then my 50 1.4 is very valuable too.

70-200 lens is one of the most versatile pieces of glass out there.

Interestingly enough, I'd have to say my Sigma 18-125. It's my least used lens nowadays, and it's my least sharp lens (though still sharp). However, it's really the lens with which my photography really grew. I'd say at least half of what I would consider my best shots were taken with that lens. While I use my Tokina 12-24, 50 f/1.8 and 80-200L much more now, the Sigma still sees use when I travel light, or if I need a middle range focal length.

Canon 24-105 F4 about 95% of the time. The image quality is superb and the IS works great!

My 70-200 f/4 is the real deal for me - wonderful lens in every way, and sucha good price I keep pinching myself - I can't believe such a good lens is so well priced within the L range. and I love how it performs, mainly I use if for outdoor portraits ( bit too long for indoors)