They're both very nice and function as you'd expect so it's kinda hard to say. The FC-187 V2 is definitely the bigger of the two, it feels heavier and sturdier than the D020-D but I actually managed to crack it during the first clean.. I guess I was shaking too vigorously with the iso/salt as a very small crack appeared about half-way down the downstem, between the perc and the dewar joint. It still works fine though and at least the perc is fixed to the bottom of the can in the FC-187 so it hopefully won't break completely. Still not sure how it could've happened really, guess I was just unlucky with this one.
I thought I'd prefer the side-car style of the FC-187 but I actually prefer the D020-D design, and I'd also say the D020-D has a more comfortable mouthpiece for me. Overall, I'd have to say I prefer the D020-D as despite it not feeling as sturdy as the FC-187, I prefer the smaller size and the mouthpiece.
Something else to note... I don't like how recessed the dewar joint is on the FC-187. When I use my E-Nano and GonG, I like to pull them both off at the same time at the end of the hit using my little (pinkie) finger to grab the GonG. Because the dewar joint on the FC-187 is so recessed, the GonG sits too deep and the E-Nano is too close to the top of the can for me to get to the GonG without taking the E-Nano off first. So when I use the FC-187 with my E-Nano, I use a 18mm male to 18mm female adapter and then put the GonG in that.
Thanks for the help. Maybe your FC-187 V2 had a slight crack in it before and you made it larger when cleaning? Thanks for the adapter tip since that is something you would find out afterwards. I still think I am going with the FC-187 V2.
Cheers