Originally posted by nayuop having the 100+ range for taking macro shots
There's no relation between focal length and macro capabilities, per se. I have a 50mm dedicated macro lens and it will create bigger enlargments than my 100-300mm lens at 300mm.
Regarding your original question, the best lens for your needs would probably be the Pentax 18-135. the Tamron 18-250 (or 270 now?) would be a good, but not great, choice optically.
A lens like the Sigma 17-70 would put you up one step in image quality, and improve your capabilities in low light (to some extend, it won't do magic). Plus it's great for macro.
If I went to Europe, I would bring my Sigma 17-70, F50 f1,7 and DA21 Limited for low light, and maybe, just maybe, consider bringing my 100-300mm tele lens. I doubt I'd use it a lot.