Go for premium potting soil. It will be full of goodness. Buying cheap soil low on nutrients just means the sales person can sell you more stuff. Get something your grandparents would buy to grow tomatoes/herbs and don't skimp on price - you get what you pay for. The decent premium types of soils will have enough nutrition in it already that you won't have to worry about feeding for 3-6 weeks (roughly) and if you are new to growing this removes a major headache for less experienced people, as a lot of problems that I see are with people over feeding their plants when young. Overfeeding when young is an easy way of killing your babies or really giving them a set back while they recover from soil toxicity.
In short - buy the best potting soil you can afford and you will have less problems in the long run. It also means you don't have to buy/spend/use as much artificial nutrients, also saving you money in the long run, easily recovering any extra costs that the premium potting soil cost you in the first place.
Hope this helps. Good luck with your grow!
... Organoman.