Different lens for different use:
-18-135 is a general walkabout lens with a good reputation, 135mm is very short for any kind of long distance shot
-55-250 is a zoom with a good reputation, 55mm is too long for general use
I have a 55-250 for a few years now and it's a great, light and cheap. I like it for wildlife, ok not amazing like a 150-600mm, but for the price, size and weight it's amazing and I've taken some nice picture with it. It's also pretty good to take picture of kids playing in the park on a sunny day and portrait of friends and family where the extra distance while shooting make you less intrusive and get the natural side of people instead of posing picture.
I haven't tried a 18-135, I read good things on hear but it's the kind of "always on the camera", "good for everything" lens while with 55mm as a minimum the other is a "specialized" lens. So it depend what you already have and what you are intending to do with the lens. For exemple a basic kit would be a 18-55 + 55-250 which complement each other.