It is so hard to qualify which robot for me is the best looking ever, but year after year this team collectively builds some of the most striking machines.
I think Recoil from team 118 and all of their robots for that matter are breathtaking when seen up close. This video form 2014 shows the construction, the quality, and the aesthetic appeal of their machine.
https://www.youtube.com/watch?v=PtRewwr59d8
This robot would be near the top of my list.
If you don't like that one, you can't deny the space age look of Apex their 2013 robot. Which has to be the best looking machine I have ever seen.
https://www.youtube.com/watch?v=DojyJ9bZ4fk