Just to share my experience.
I acquired the T3i 18-55 two years ago and started to “collect” lenses.
I first went to the 70-200 F4L mainly because I wanted high quality and the size does match very well the camera.
The image quality is just excellent
But if I would do it again, I would go for the 70-300L as you never get enough reach
I considered the EFS 17-55 F 2.8 which I tried and is extremely good, but after spending too many time on this addicting forum, I thought I would go Full Frame at some point (I just received my new 6D last week).
My next lens was the Macro 100 F2.8 L IS. I thought the 70-200 was sharp but this one is just answome. Very good purchase
I also have the Shorty Forty and I love it with the T3i as a walk around. You can’t get sharper for 149$. With it, I use Microsoft ICE for Landscape and I am very happy with results.
I try to avoid GAS (see other thread) but visiting this forum help in deciding what I need.
So, as some mention, think about what you shoot and select the tools for that.