Michael Feingold is the only writer today I can think of who is actually a critic, rather than a reviewer. He doesn't just say whether something is good or bad. He puts works of art in a cultural context. I always enjoy reading his perspectives.
As for reviewers, I think Jesse Green and Alexis Soloski are the best writers currently in the game, but I don't go to anyone for specific advice about whether to see a show or not.
"You travel alone because other people are only there to remind you how much that hook hurts that we all bit down on. Wait for that one day we can bite free and get back out there in space where we belong, sail back over water, over skies, into space, the hook finally out of our mouths and we wander back out there in space spawning to other planets never to return hurrah to earth and we'll look back and can't even see these lives here anymore. Only the taste of blood to remind us we ever existed. The earth is small. We're gone. We're dead. We're safe."
-John Guare, Landscape of the Body
Honestly, WhizzerMarvin as well but if we're talking publications, I agree with Ben Brantley about 95% of the time (and love his writing), so I'd have to go with him.
I'm with denali.fire. I honestly think people are crazy to rely so much on the opinion of "the chosen few" critics. I research shows and if the subject/material and cast/creatives interest me that's what I see!
But the the days of one critic wielding make or break power over a show's success are long past us. The Kerrs, Atkinsons, and Barneses are just theater names now. I'm guessing that this comes as a relief to the current crop of critics.
And of course in those days theatregoers didn't have the internet to learn about shows. All they had were reviews, the cast album, and maybe an Ed Sullivan performance (and later the Tony performances too but those couldn't always be counted on). The world really has changed a lot in that respect.