The Dark Knight wrote in post #17280643
I use my SL1 as a travel camera, and with the 55-250 as an inexpensive way to get reach when I want it.
I'm considering giving up the 18-55 STM and the 55-250 (non-STM) that I got as a kit and getting the 18-135 as a "1 lens solution" for traveling with.
I'll lose a lot of reach, but when I consider I still get almost 200mm in 35mm equivalent terms, seems enough. I'm considering the 18-135 STM as it seems to be the best IQ of the superzoom EF-S lenses.
Thoughts?
I am in a similar situation.
The info I have got from the web says that the 18-135mm STM is a good lens, but not a great lens. I think the 18-55 STM and 55-250 STM would outperform it. The two lens kit also has quite a bit more reach, but I don't use 135-250mm that often, so that is not that important to me. The single 18-135 would be more convenient, though.
Weighing these factors, I have decided to stay with the two-lens solution. That's partly because I already have those.
In your case, your 55-250mm is not an STM, so that might tip the balance if it were me to the 18-135mm STM.
(And the 35mm format has no bearing at all on this issue!)