Here too lots of opinions, none of which would be the wrong answer. Here are my opinions:
16'
small, versatile, easy to tow with even the most modest vehicle Has a bumper. I believe these have front rock guards.
17'
same as above but no bumper (but I did start to notice that bumpers may have started to be added). I have not seen front rock guards on these models
Here is the rub so to speak. I had a 19' Bambi, a 2003. If your lifestyle includes a significant other and a pet, you will be fairly cramped with space and such, even with a 19'. This by no means suggests you run out and get a 34' slide out
, but I am here to share with you many an Airstreamer who with the best of intentions started out small because it was cute, able to tow with a wider range of vehicles, etc, then after the first year or two, the glow faded and reality set in. Airstreams are measured from hitch connector to rear bumper. From what I've seen, you loose about 3' of what is listed as it's length, so a 16' unit has about 13' feet of internal living space.
If you don't take a lot of stuff with you and/or you don't have a signficant other that goes with and/or you don't have a pet that is 30lbs or larger, perhaps these might just be a good size for you.
I had a 65lb shepard and with my significant other, the 19 footer showed it's limitations early on. As one of those mentioned above, I bought the 19' because we liked the floorplan, it could be towed easily with what I had and of course it's a cute little Airstream. In reality, I needed a 23' to 25'. Since the 23' was not around in 2004, I went with the 25' unit. That decision required me to upgrade my tow vehicle, but it has been a decision that fit my actual needs for RVing.
Today, I no longer have my 65lb shepard, but I still have my significant other and now two 25lb terriers and we still have lots of room (even with everything *she* packs).
All that said, if the 17' had a bumper, I would go for that size because it is slightly larger and it does not appear to have a "wet" bath. I would however add front rock guards. Mine on both units took many hits for the team (flying rocks off the rear tires of the tow vehicle).
My advise is to be true in what you need when you camp and to take into account what might be needed 5 years from now because upgrading can get expensive (ask me how I know).