Possible Duplicate:
What is a good general purpose lens for Canon?
Which lens should someone who enjoys the Canon EF 50mm f/1.8 get next?
I have recently purchased a Canon 600D (body only) and a Canon 50mm 1.8 II. I am trying to decide which 'general purpose' lens to buy. I want a travel lens (I definitely only want to travel with 1 lens though would consider also taking the one Ive already got given it is small), plus I want to be able to take some landscapes when hiking, family photos and shots of my young son.
I am currently looking at the Canon 15-85mm or the 18-135mm. Budget wise would prefer to spend less rather than more, but I want to be able to stick with this new lens for a while as I don't know when I will be buying any more so want to buy right the first time.
As a beginner would I notice much difference in IQ between these lenses? Would the IQ on the 18-135mm be a disappointment after using the prime I already have? Would the extra zoom in the 18-135mm be better for portraits and candid travel shots? Any advice much appreciated!