After that, I will take on DS9. It's the only piece of Star Trek I haven't watched, surprisingly (It never aired on my local tv channels back when I was young, so I haven't gotten any personal attachment to it).
Go watch DS9 ASAP sir!
Right now i am at the begining of 6th season. My 2nd rewatch of entire series. First season or two is not that great but after that you'll love it forever.