For sheer quality, the EF-S 15-85. It's a much better lens than the 17-85, as well as being significantly wider, and is of L quality. The 15mm at the wide end is more useful in many ways than the loss of length as the better IQ allows you to crop. Also, its size is suitable for the small camera. The 70-200mm f/2.8 would not seem suitable for a girlfriend to carry around on the lightweight body, or indeed the 70-300L. But, the 70-200 f/4 IS might just be, and its IQ is very, very close to its larger brother. The 55-250 is small, lightweight and incredible value for money for quite good performance.