I ain't no expert here but,Hook is right alot depends on What your planting and the Soil it is going in.
A Soil Test would tell you the best type to use for what your planting.If time dosen't allow for a good send off soil sample test there are some self tester kits around at some seed/garden stores. I have never sent one off but have used the self test kits in my garden,however I can't say how accurate it has been compared to the other,but the garden grows well.
If your using a commerical seed blend most of them have Fetilzer recommendations on the bag. ;)