I've not used the 17-55, but by all accounts it's an excellent piece of glass for DX bodies. The 18-200 on the other hand is 'ho-hum' at best. It's poor at both ends of it's focal range, has lacklustre build-quality, and is really a 'Swiss-army lens' (It does a lot of things, but none of them very well). That said, it really depends on your shooting style and subjects. I would never recommend buying any 'cheap' lens, but Nikon has built some really nice 70-300s that can be had used for relatively little money.