my personal view on the topic ....
go to a shop with decent range of boards, try some out, find a flex that you think feels cool, not too stiff, but not too soft either, find a length you like, longer = smoother cruising/carving but harder to slide and bulkier to cruise with from place to place where you'd have to carry/store it occasionally .....
also, don't be tricked by people breaking down entire brands because they stood on one bad board of said brand ...
last month i've had the opportunity of hanging out with a pretty large group of longboarders and try out a wide array of boards, ranging from super short carvers to long smooth pintails, dancers and even a super stiff handbuilt carbon dh board
I personally really enjoyed the loaded tan tien and dervish, together with my own sector 9 uluwatu bamboo
if you have a chance, and know a group of longboarders or something, try to meet with them and ride some of their boards to get a feel of what you prefer ...
also another sidenote, keep in mind a longboard is quite an expensive investment and winter is in front of our door, so maybe you want to postpone it a little and spend the money on skiing, then in spring, look for a board ?
good luck with the stoke, it's a really fun pass-time and way of transportation in general !