I just came back from a trip to Epcot with my family. I brought a Canon t2i, 15-85, and a 55-250 (this is the best travel telephoto! Its very light, good range, and pretty sharp)
However I also realize that the 15-85 range is amazing for travel!! My 55-250 was put on once, for a couple of shots, just because I had it.. but really could of lived without it.
It really depends on how you like to shoot. I took about 500 shots in 1 day
I did an analysis of my ranges with Exposureplot (very good software to determine how you really shoot)
- 50% of my shots were below 38mm. That means that on a crop the 24-105 would not be useful since its really (38.4-168). I would definitely need a 10-22 but then I would of had to keep switching lenses!
- 26% of my shots were below 27mm and 15% above 88mm. That means I would of lost those 41% if I brought only 17-55. Or would of had to bring 3 lenses to compensate. (10-22, 17-55, 70+)
The only challenge was indoor shooting and night time! Looking back I think maybe 15% of my shots were low light. So if that is more of a priority for you then maybe you have to look at other options.
The indoor ride pictures were at f3.5 and still hitting 3200 ISO and were not that great.. so f2.8 would likely not help. Only a prime might be better but then indoors you have limited choice of movement and distance.
The restaurant and other general indoor pictures would of likely been better with a f2.8 but I am not sure by how much and would it really of made that much of a difference for me considering its a small percentage.
Like I said.. it really depends on your priorities and how many lenses do you want to carry !!
If I knew that I was going on a trip primarily to a museum or lots of indoors then I would take a 17-50 f2.8.
However for general site seeing with minimal weight and lens changes you cannot beat 15-85!