The 11/16 build will have an active spoiler that lowers a little at higher speeds and tucks away when parked, which looks nicer (to me) and provides visual confirmation that the car is locked.
The 6/17 build will have a fixed spoiler.
As much as some people say they don’t like the active spoiler, I remember seeing a poll on the forums here showing >3/4 of respondents preferred the active spoiler if they had a choice.
The 11/16 will also come with perforated/vented (albeit a little weak when compared to other car manufacturers’ seats), real leather seats. They switched to smooth, non-perforated, vegan seats in 2017. Personally, I like the perforated real leather seats better than the smooth fake leather. We have an infant and toddler, and not a single problem with the perforated real leather seats. The real leather seats seem thicker.
Regarding build quality, that’s just a luck of the draw ever since the beginning of Tesla IMO. I’ve seen used cars and brand new cars built these days that are both perfect and flawed when I was at the delivery center. This was also the case for us when we bought new and used Tesla. Our used was perfect whereas the new required various repairs.
Maybe one thing to look into is whether the 11/16 or 6/17 has ludicrous. Since you are buying used, check to see what the 0-60 time is on the listing. It will be either 3.1 or 2.8 seconds. Tesla does not factor whether a used car has ludicrous option into their used car pricing/listing. So, it’s basically free ludicrous if the particular used VIN has it. There is a (relatively) significant difference in acceleration between having ludicrous and not.
From my own used purchase research, Tesla also does not seem to factor into pricing whether a used VIN comes with 22” or 20” wheels.