Definitely should. Based on the quality and content of the various romances I believe Liara to be the "default" romance, it is definitely the most satisfying to me.
My last playthrough I did Tali which I had never even really put any thought into before (I mean she's stuck in a biohazard suit, who knows what's under there?) but it was actually very sweet. She is a real cutie.
Too bad we can't get too see what she's working with under there. Ash got a boobjob and a new haircut in the 3rd, can't let that go to waste.