I have both the EF-S 17-55 f/2.8 and the EF 24-105 f/4 with a 7D
For indoors, I will put on the 17-55. It is a bit wider, and one stop faster. Most often I can get away without using a flash. Plenty wide enough as well.
For outdoors / walk-around, I use the 24-105. On the wide end I am never constrained (easy enough to take a step back if needed), and the longer reach is preferred for me.
Like Nero I would first recommend the 17-55, however, since you have the tammy in a similar range, I would definitely go with the 24-105L
Although the 15-85 is a very sharp and well made lens, I do not recommend it for a few reasons.
- Inside it is not very fast - unless you don't mind using a flash all the time (I had a friend that sold his after trying my 17-55 at an indoor event)
- outside I would rather have the reach on the long end vs a bit wider, and weather sealing.
- As you mentioned, an EF format lens will carry over to FF if you go that way