David,

I read your post and said, "Hey, that's me!" I also have a T1i with the 18-55 IS and 55-550 IS. I too will be upgrading to the 70D. I do not have experience with any other lenses but a question I would as is, "Are you happy with the results you are getting now?" I imagine the answer is no or why would you upgrade? So what are you not happy with?

For me the 70D became my upgrade choice for a couple of reasons. First, the auto focus (including the Dual Pixel AF). I have been longing for a better AF to capture my kids. The kicker is that the camera is just half of the equation. You also need a fast focusing lens, which I don't have. Both the 17-55 and the 15-85 are faster with USM than STM. So the lens choice is not only about IQ. Second, the DPAF. I always have a Canon HD camcorder and I am switching between the two constantly. With the 70D this switch will just be a switch. However, I plan on having the 18-135 STM be my go-to lens for video for the smooth and quite focusing. The third reason is the 7 fps. My sister got the 7D when it came out and I wanted it (but the wallet couldn't handle it ). The 70D comes very close to the 7D's 8 fps at the lower price. Other reasons for upgrading is the WiFi, better build, flash transmitter, etc, etc.

Here is what I am doing. Depending on your needs it may not be ideal, but I believe it will work for me. I will start of with the 70D with 18-135 STM. I will have to begin saving again and will get the 70-200 2.8. I am going with the 2.8 because I want it fast for my fast moving kids and I want the 2.8 to improve the AF at the center point (where I do most of my focusing). I am not getting the 70-200 2.8 IS II because it is way out of my price range. Next I will save for the 17-55. With the recent price drop it make is more reasonable. The 2.8 again for fast kids and better AF. Then I want the 100 2.8L macro. That might even come before the 17-55. I love macro and currently I use the 55-250 with the 500D macro lens attachment. Even with these other lenses I will keep the 18-135 for video and travel.

I don't know if this helps much but I thought I would share since I am in a similar situation.

All you more experienced photographers, please let me know if any of my thinking is flawed!