I run Xubuntu on a 13" MacBook Air, which is only ~$1100 and does everything I need. For web developers, I feel like the Air is almost the default option. That your budget is so high (“under $1700” would seem to include the vast majority of laptops) suggests you may be doing something that needs serious CPU/GPU performance, in which case our goals are different.
For me, portability was paramount (otherwise why get a laptop?), so I wanted it lightweight and no bigger than 13". Second, I wanted it to have an SSD so it'd be fast. I had read that replacing hard drives with SSDs makes a huge difference in responsiveness and that turns out to be absolutely true. All other specs (CPU, RAM, ...), I didn't care about because I felt confident they would be good enough.
Those goals narrowed it down to either one of the PC ultrabooks (which System76 does not make, unfortunately) or the Air. Out of the PC ultrabooks, the ThinkPad X1 Carbon was the best contender, and w1ntermute's comments in this thread: https://news.ycombinator.com/item?id=4849781 have convinced me that if I were buying a laptop today, I'd probably pick the X1 Carbon over the Air. Either one's great, though, and supports Ubuntu just fine.