Which lens has brought you the most...?

Sigma 24-70 EX DG definetely.

Every time I take it, I'm amazed by the clarity and accuracy of focus.

300 f/2.8 IS -- sometimes it's the only glass I take to a baseball game.

Definately the 135L, but the 85L when I had it for a short time, just amazing. Nothing else brings me joy than those 2 lenses. The 85 1.8 is fantastic, but the 85L just has that magical image.

The single lens?
500mm f/4L IS

IF I look at via timeline, ei, what made me happiest at the time, vs. overall it was;
Bigma --> Sigma 500mm f/4.5 EX, --> EF 500mm f/4L IS

70 - 200 hands down

and you just got it 5 minutes ago.

Canon 17-85 - my first IS lens - versatile and sharp

Tokina 100mm f2.8 macro, closely followed by the 70-200 f/4L. But I know that both will drop in rank as soon as I get the new 400 f5.6 IS (yes, I'm holding out hope . Please Canon!!!)

100-400 for sure!!!

got to be my 70-200L

Hmmmm, this is kind of a hard question for me. It's sort of like asking a carpenter which tool made him happiest about his carpentry

The lenses I have I use/choose for the most appropriate circumstances. The one I expected the least from and was most pleasantly surprised with was the 24-105 f4L. It's a great lens.

I bought it for a specific purpose (fair and festival photography), but I was doubtful about the range and it's ability to work within my style of photography, and I was fully prepared to return it to the store if it didn't work out. To my delight, it is almost the perfect lens for the purpose for which I bought it. I'd like to think it was my photographic acumen that made me choose the lens, but it's more likely just dumb luck.

Mark

24-105 F4L

Really hard for me to say...I've spent enough time collecting what I have and researching them prior to purchase, that a lot of them give me the WOW factor after looking at a shot. I'd have to say it's a tie right now between my 85mm 1.8 and my 30mm 1.4. I've had the 1.8 a bit longer so it's right up there with the most impressive results as there's more to compare to. I know the 30mm 1.4 will surpass it though as just in one day I'm completely blown away by the performance.
With all that being said though, my 10-20 is a damn fine piece of glass. You know, honestly it's best to say it's a three way tie right now...

IQ happiness would have to be the 70-200/2.8 IS.

General enjoyment shooting the kids (hey now!) would have to be the 17-85.

If I could get them to stay at least 10 feet away at all times I could probably drop the 17-85.

135L is my favorite picture producer thus far! I really love it