If you're going to take the time to learn an opening...

There is a lot to be said for new players learning a system that avoids a lot of book lines, but at the end of the day, systems are less than the best.

So when the time comes to study openings the right way, what are the best openings and defenses to know completely? Or does the answer depend on each individual?

I basically do not want to spend any significant amount of time learning some inferior openings and defenses just because they are easier to learn. If I'm going to learn it the right way then I want to learn something worthwhile.

The easy answer is to play what everybody plays. Spanish, Italian, Sicilian, to name a few. You might be able to get by with weird things like the hippo or 1. Na3, but there is a reason that the most common openings are... common. Learn the basic ideas, and that's enough opening study to last most people a lifetime.

Right now I am working on Watson's understanding the opening series.

It's more important to be able to develop in a way you can understand and get into the middlegame. There aren't many openings you can't play at club level. I mean 1.h4 is probably pushing it a little.

I find it quite amusing how every book that covers any opening that isn't the MOST popular opening preaches how much time you are saving by choosing it.  Seems like every repertoire book that avoids mainline stuff has a few obligatory introduction pages on why tackling the mainline is dangerous, involves learning too much theory, or your opponent will know more than you anyway.  It's silly.  After I watched Carlsen's brilliant use of the Berlin defense in the world championship I decided to give it a try for the first time in years.  My first game with it I beat a player rated about 200 points higher than me.  Openings are important but they are very little in the grand scheme of things at my level.  And if they mean very little at my level you can bet your life they mean absolutely nothing at your level.

Play a *sound* opening that you enjoy playing with and perform well in and you'll be fine.  The mainline stuff is obviously good, but there are other lines that are almost as good that aren't explored as much.  It's up to you if you want to take the time to experiment with these obscure lines or not.

I don't even agree with beginners using "system" openings I think they are a complete waste of time and they inhibit chess development.  The problem with system openings is that the player gets lazy and is just setting up their pieces in the opening rather than playing actively against their opponent and trying to achieve a concrete goal.

In my opinion beginners should learn basic opening principles of development and central control as well as typical tactical themes in the opening.  Once you improve a bit you should learn the mainlines of important openings and the ideas behind the moves.  At a much higher level (I guess around expert or master) you will probably have to start learning specific variations in much more detail and putting together a repertoire.  

At my level in OTB I can confidently say that if I play an opponent of similar strength I could play pretty much any opening (including those that I barely know) without it having much bearing on the result.  I do buy opening books but only as reference materials for playing correspondence chess and for general interest, I don't actually invest time in learning alot of variations.  

Sicilian, Spanish... You suggested the opening with more theory to learn

In my opinion in games between players <2000 elo you can play even the sharpest openings without knowing the theory as long as you take some time to think during the opening.  I've played against a couple of players who were stronger than me and didn't know any theory at all, not even mainlines of major openings.