A couple things to add that I haven't seen discussed so far in this thread:
1. The right ratio to use will depend on the soil or mix to which it is being applied. If the soil already has one of the 3 primaries in abundance, then it doesn't need as much of that. So you should consider the composition of your grow mix. For example, the commonly used 5-1-1 frequently may contain pine bark that may have been composted very little or not at all. The microorganisms that decompose this may consume available nitrogen. In this case you'd need to make sure your mix has a high percentage of N.
2. It would be grand coincidence if 10-10-10 fertilizer were truly "balanced." What's a more balanced diet, 10 hamburgers and 10 pieces of corn, or 1 hamburger and 100 pieces of corn? The point is, a balanced fertilizer is one that contains the same percentage of nutrients that the plant actually uses. Of course studies have been done to determine what that is, but I don't know if there is a scientific consensus (probably there is, I just don't know what it is). My opinion is that Miracle Gro probably comes closest to this in most situations, and it is 3-1-2 (or 9-3-6, etc). But certainly there may be other studies or opinions that have merit as well.
3. Even if you use something that is not the ideal ratio, the excess unused nutrients will likely be rinsed away before they cause any harm to the plant, as long as you don't "burn" the plant by using too concentrated a fertilizer. That's why 10-10-10 probably works just as well as 9-3-6.
4. Think about if you want mycorrhizae. Might help uptake of available nutrients. Some folks swear by it.
5. Think about trace elements. There are several other minerals needed in small quantities. It's likely that most commercial mixes have these added. I don't know about pine bark or peat moss. Somebody should investigate if that mix might be deficient in a minor requirement. If you are concerned, there are weak fertilizers that have the minors in sufficient quantities that can be added to the mix up front.
6. Think about pH. This influences how well roots can absorb what's there. I believe that if you use a liquid fertilizer mixed with water, the pH of this fluid will be near 7, and will be absorbed short term regardless of the pH of your growing mix. In other words, if you liquid fertilize once over week or two, this could help compensate for too high or low pH. A plant does not need to be fertilized every day. More like a reptile than a human.