What you woul recommend: It is after all a community decision.
The open discussion thread was mainly for people that want to share other ideas for the community mod. For example if someone was working on a galactic map and wanted to include it into the mod or if you had an idea for the music etc.
My 2 cents, i would suggest voting occur in the competion thread because it will help keep it towards the top and its easy to navigate when looking at ship designs.
I also hope that when people vote they will also include any constructive criticism for the designers to read and maybe to help designers tweak their designs.