Read an article in the Wall Street Journal about the death of the slushpile. It's pretty poignant for an aspiring author to read that the slushpile is considered dead and that publication through that means is becoming less and less likely. Of course, there are still success stories, like Stephanie Meyer, but it sounds like the more accepted approach is to get an agent first. Orson Scott Card gave different advice in his book. He said get the agent after you had an offer to buy your work.
I guess the best thing is first, to write something that is better than anything in a "slushpile" but secondly, we have to decide if traditional means best.
Maybe the actual best way to do things is to build a resume before seeking publication from a large firm. Maybe if you bring a dedicated group of rabid fans, then you won't have to worry about slushpiles and all the rest.
I would say the best thing would be to create something first. Get 1000 fans. Then have an agent come find you.