I think you should get whichever looks best with your town, even if you don't have a theme. Do most buildings look more classic or more modern? Are you planning on getting train station or town hall upgrades?
Honestly, there's no point making a poll... we all know Booker/Classic will probably win. :b
I'll take the road less traveled and vote Copper/Modern because it's like the old Gamecube station. (In fact I thought at first that's what the 'Classic station' meant.)
I personally prefer the modern style of the station and I actually like Copper better. Unpopular opinion though, and the modern goes with my theme better.
personally i prefer cooper, so i went with the modern police station. i think you should pick which station that would look better in your town, but also you could flip a coin or s/t if you're that indecisive. D: i don't know why they had to separate them...
I also like the look of the modern police station best. However, I wish I didn't have to choose between Booker and Copper.
Go with the one you like best, because it's ultimately your town and it needs to make you happy. You could always choose to wait before building the Station, develop your town more in case a theme pops up and you don' regret being stuck with one or the other.
