If you would hav only one lens....

I am new into photograph (about a year), I have a 450D and the kit lens.
I am quite ok with what I have, have used it for every day photos and travelling. I am not into zooming .
I have bought a nifty-fifty and I descovered that I would like more background blur... but I hate changeing lenses (I think because I am to lasy to change lenses I have used the 50mm only 3 or 4 times)

This year I want a new lens and I can't decide what I want...
I am in between 17-55 2.8 or the 24-105 4.0 ... My perfect renge would have been the 15-85, but I would like a bigger aperture...
Beining so much money I am trying to think it seven times before spending once. Would I miss the wide angle 18-24 if I go for the 24-105?

For indoor shots I have a 430ex wich is really worth it.

(uploaded 2 random photos taken with the kit lens )

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If you like a smaller depth of field, you'll appreciate the larger aperture of the 17-55 f2.8.

I'm guessing that by "I am not into zooming" you mean you don't need a long focal length lens since all the lenses you've short-listed are zooms.

The 24-105 is f/4, which won't be good for your ambitions for shallow depth of field.

Best bet is either the 17-55/2.8 IS or the Tamron 17-50. Current word around the camp fire is that the newer VC version is not as sharp.

if i could only have one lens on a crop body; 24mm f/1.4L
or 35mm f/1.4L on full frame/1.3

17-55 2.8 IS. It's the best general zoom for a crop in my opinion

Judging by that duck shot, you really need to switch out that kit lens.
Personally, I like telephotos, so the shortest I would ever go is maybe 50mm, but yeah, the 17-55 2.8 IS would seem right for you if you like to take wide-angle pics.

Here's a duck at f/1.2

I haven't a talent to explain very well... I meant I am not into telephoto, I don't really want much more than 55mm ... 85 probably would be perfect, but i don't know if it's worth it to give up the wide angle.
I am not that good a photographer yet to use primes, I just feel the need to twist it to fit more tha to try to go 2 steps behin (in the street) to fit more.

So the 17-55 2.8 get's the most votes...

Tharaka wrote in post #9459223
if i could only have one lens on a crop body; 24mm f/1.4L
or 35mm f/1.4L on full frame/1.3

As an answer to the title, the 35mm on FF or 24mm on 1.6x would be my choice for just one.

Reading the OPs post though, I think for crop the 17-55IS is the answer. Tamron 17-50 if cash is more of a concern than USM or IS.

Since you are more into wide angle and less into telephoto, I'd consider getting another camera body that would allow you to capture a wide photo. As you probably already know, your 450D is cropping your photos right out of the gate by virtue of its sensor size. If going full frame is not an option for you then I'd suggest you look into the 24-70L. Actually, I'd suggest that lens even if you can get a full frame body.

Benandbobbi wrote in post #9459748
Since you are more into wide angle and less into telephoto, I'd consider getting another camera body that would allow you to capture a wide photo. As you probably already know, your 450D is cropping your photos right out of the gate by virtue of its sensor size. If going full frame is not an option for you then I'd suggest you look into the 24-70L. Actually, I'd suggest that lens even if you can get a full frame body.

Well, an upgrade to FF would mean getting a whole new camera+lens.
I would find it logical if more people used primes on the wide end (<35mm) as wide-angles are harder to make and keep optically good, so a 24L for example, would beat a 24-70mm or 16-35mm in spades, especially where distortion is concerned.

You don't have to be good to use primes, just get the ones that feel natural for you. I have a 70-200 zoom, but use it mostly at 70-90mm, and 200mm, so I could replace it with just 2 primes if I wanted to.
As always, I suggest people to take a look at ExposurePlot which shows you a graph of focal length usage. So if you see that you mostly use your zoom at say, 24 & 50mm, you probably wouldn't miss anything by going to a 24L + 50 1.4 prime set.

Thanks for that program , very very interesting, it really helped taking out the 24-105 from my list... as 35% of my photos are at the 18mm end and another 40% at 50-50mmm leaving the small rest somewhere in between or crops.
So I have a new invention ideea: my ideal camera would be one that has 2 prime lenses .... more convenient to use than 2 camera for event photographers too... I hope that the marketing people from Canon read this forum

Now back to being serious: I don't like to switch lenses so this takes the primes out of the discusion. (I guess I am lazy or just amateur, but I use my camera on going in trips or in the with friends and it would be a pain to take a landscape photo and put the bag down and change the lens to take a portrait of a cat/dog/friend and change back when you see something else... grrr...)

I don't think I can give up IS so the Tamron is out of the discussion... change the body + lens is way too expensive for me .... so this leaves me trying to save for the 17-55 I guess...