I want a better lens than the stock lens I've been using for the last year and a half. I know the 18-200 is the most practical everyday purchase, and also the most affordable. I just keep this about how fast the other lens is comparably. The faster lens would be good in darker situations, but I would continue without a zoom. Hmm... Maybe, I could get the 18-200 and a faster prime...
Josh
Josh, if you are craving better glass then you should get the 17-55. It is everything they say it is.
If you are craving extra reach, then get the 18-200. I will tell you that I own the Tamron 18-270 which is a pretty well-reviewed all-in-one lens. But since I got the Canon 17-55 f/2.8, I have put the Tamron back on my camera only a few times. I'm too spoiled by the IQ of the Canon.
If you have nothing else beyond that 55mm reach, then you will have to address that at some point. But if you want better glass, you will likely still want better glass after buying the 18-200.
The primes are great but be careful choosing the right length for what you want to shoot. My first prime was the 50mm f/1.8. I've only used it a couple of times. I greatly prefer the Sigma 30mm f/1.4. I guess I should since it cost so much more. (Mostly I just like the 30mm length compared to the 50mm length). The more expensive Sigma 30 was a much better investment for me than the $100 I spent on the nifty fifty since I never use it.
I'm the one always saying the most expensive lens is the one you buy twice. My point is that if what you buy does not ultimately meet your needs or satisfy the desire for what you were seeking, you will likely be shelling out some more dough very soon.
FWIW........ there are less expensive options for a faster 17-55ish lens. Tamron makes one as does Sigma. I did a lot of research on this before committing to the cost of the Canon lens. The Tamron non stabilized version is very will reviewed here on these boards. But the focus motor is annoyingly loud. And the last thing I needed was my kids hearing me focusing the camera on them. The teens would probably be gone before I got off a shot. But it's said to be a very sharp lens. They do make a stabilized version of this but it is said to have lost some of the sharpenss that lens was known for when they added the stabilizlation. Since I have rather unsteady hands, I did know I wanted a stabilized lens.
Good luck with your choice. Be sure to let us know what you do!