Ruy Lopez

Which ever you prefer. None is better than the other if you understand what you should be doing and are able to play good chess.

Just seems like there is a lot of extra theory associated with the Ruy compared to other openings.

That's probably true so it's up to you. You can try to absorb all the different ideas or never play a ruy lopez in your life. If you are playing a serious tourney soon and have never played it I wouldn't advise you to unfurl your first ever ruy in game 1. But I would advise you try out the opening over time in less important settings just to broaden your overall play.

"Of all chess openings, the Ruy Lopez is one of the oldest, best and most analyzed." - FM Carsten Hansen (2010)
"Alekhine advised beginners not to play the Spanish game. We also recommend you get some experience first by playing relatively simple openings - the Scotch and Italian games - and only then move on to the Spanish one." - Journey to the Chess Kingdom by Yuri Averbakh and Mikhail Beilin

Possibly helpful:
The Four Knights: Move by Move by Cyrus Lakdawala (2012)
https://web.archive.org/web/20140627040728/http://www.chesscafe.com/text/ebcafe06.pdf
https://web.archive.org/web/20140627104938/http://www.chesscafe.com/text/hansen159.pdf
The Ruy Lopez: Move by Move by Neil McDonald (2011)
https://web.archive.org/web/20140627022042/http://www.chesscafe.com/text/hansen153.pdf
Playing 1.e4 - Caro-Kann, 1...e5 and Minor Lines by John Shaw
http://www.qualitychess.co.uk/ebooks/Playing1e4CaroKannandothers-excerpt.pdf
My First Chess Opening Repertoire for White by Vincent Morethttps://www.newinchess.com/media/wysiwyg/product_pdf/9033.pdf
A SIMPLE CHESS OPENING REPERTOIRE FOR WHITE by Sam Collins
http://www.gambitbooks.com/pdfs/A_Simple_Chess_Opening_Repertoire_for_White.pdf
Winning with the Slow (but Venomous!) Italian by Karsten Müller and Georgios Souleidis

https://www.newinchess.com/media/wysiwyg/product_pdf/9037.pdf

 Thanks for the recommendations kindaspongey.  I think you can springboard off the Italian Game to the Evans Gambit after you have it.

This is an often recommended and very good book:
https://www.amazon.com/Mastering-Spanish-Method-Batsford-Library/dp/0805032789

Instead of trying to learn many variations, you learn the underlying ideas, so you can have the right approach towards many different variations, even if you don't have any experience playing against them.

And your opponent's face the same difficulty. They'll know a few main lines well, a few sidelines not as well, and many sidelines not at all.

I think I like the fact that Reuben Fine, in his Ideas behind the openings identifies the Italian Game and the Ruy Lopez in his reprise of e4 e5 openings as staying within the theme of preparing a well timed d4 for white.  I think I'll start with the Giuoco Piano and then move to the Ruy Lopez.  Thanks for the book recommendations. 

I've always struggled with deciding what to play in this setup and have dabbled with the Ruy, but for some reason never showed an interest in the Giuoco Piano.  After some research, it looks like very interesting possibilities abound and it solves a problem I've had with respect to my responses in my repertoire.  Hopefully I can get some experience in practical play using it so that I can understand the underlying themes and learn from some mistakes and research the opening so I can learn it well. 

Thanks for the recommendation Sammy_boi.  This looks like a good way to approach the Spanish without having to endure reams of analysis I may never remember.

You could play the exchange. Then you don't have to worry about the 1000 other Lines that come after that.

The exchange is my line.  Unfortunately, so many people try to avoid the Ruy that I have played the exchange once since trying it out and the rest of the time it's some alternative to avoid a6 after Bb5.  Usually the Schliemann or the Berlin Wall.  It was hard to lust after the advantages of the exchange variation when you're never playing it so I've been wanting to go in a different direction.

I have been playing the Italian/Giuoco Piano and liking it.  Some people think it's a flash in the pan, with not as much chance of long-term advantage as the Ruy Lopez, but I haven't found that to be the case.  You do have to be careful, though, as the early fireworks can be in Black's favor if White makes an inaccurate move or two.  (This is particularly true if Black goes for the Two Knights, many lines of which are razor sharp.)

The Evans Gambit is a fun tool to have in your repertoire.  I like to play it vs. kids as they often seem uncomfortable with it.  I won a game vs. local prodigy Jason Yu in which I did not get an immediate attack, nor recover my pawn, but his knight became stranded on the queenside and I slowly built up an unstoppable kingside attack with my "extra piece."  (Admittedly that was a few years ago, which is forever for someone like Jason--I probably wouldn't have it so easy today.)

I would guess that which opening to choose probably rates highest among most intensely thought about useless questions.

Pick something not inane (at least some GMs are willing to play it against peers) and then learn about it. Generally speaking, in the long run a different opening isn't going to give you better or worse results.

A lot of GMs play the Italian, with c3+d3. It's quite a good opening.

It's pretty boring, but they manage to squeeze some play of it now and then