Best Openings for Learning?

I used to play chess when I was a teenager, but I've forgotten a lot. I want to improve again. Which openings should I study? Which are the most educational for white and black?

ruy lopez white.. sicilian black

You should study chess tactics, i.e. the things which will win and lose you games, rather than the opening which for the moment is not all that important, until you are a bit stronger than you currently are. 

"... for those that want to be as good as they can be, they'll have to work hard.
Play opponents who are better than you … . Learn basic endgames. Create a simple opening repertoire (understanding the moves are far more important than memorizing them). Study tactics. And pick up tons of patterns. That’s the drumbeat of success. ..." - IM Jeremy Silman (December 27, 2018)
https://www.chess.com/article/view/little-things-that-help-your-game

"There is no such thing as a 'best opening.' Each player should choose an opening that attracts him. Some players are looking for a gambit as White, others for Black gambits. Many players that are starting out (or have bad memories) want to avoid mainstream systems, others want dynamic openings, and others want calm positional pathways. It’s all about personal taste and personal need.
For example, if you feel you’re poor at tactics you can choose a quiet positional opening (trying to hide from your weakness and just play chess), or seek more dynamic openings that engender lots of tactics and sacrifices (this might lead to more losses but, over time, will improve your tactical skills and make you stronger)." - IM Jeremy Silman (January 28, 2016)
https://www.chess.com/article/view/opening-questions-and-a-dream-mate

Perhaps it would be a good idea to start with Discovering Chess Openings, a book about opening principles.
https://web.archive.org/web/20140627114655/http://www.chesscafe.com/text/hansen91.pdf

Here are some books that set out to help the reader to choose specific openings:

Openings for Amateurs by Pete Tamburro (2014)
http://kenilworthian.blogspot.com/2014/05/review-of-pete-tamburros-openings-for.html
https://chessbookreviews.wordpress.com/tag/openings-for-amateurs/
https://www.mongoosepress.com/catalog/excerpts/openings_amateurs.pdf

First Steps: 1 e4 e5
https://www.newinchess.com/media/wysiwyg/product_pdf/7790.pdf

https://chesscafe.com/book-reviews/first-steps-1-e4-e5-by-john-emms/

First Steps: Queen's Gambit

https://www.newinchess.com/media/wysiwyg/product_pdf/7652.pdf

My First Chess Opening Repertoire for White
https://www.newinchess.com/media/wysiwyg/product_pdf/9033.pdf
https://chessbookreviews.wordpress.com/tag/vincent-moret/
Opening Repertoire 1 e4
https://www.newinchess.com/media/wysiwyg/product_pdf/7819.pdf

Yasser Seirawan's Winning Chess Openings
https://web.archive.org/web/20140627132508/http://www.chesscafe.com/text/hansen173.pdf

I guess 1.e4 as white and 1..e5 as black is the way to go if you chose an opening for education. King's Indian as black vs 1.d4 is a good school also. BTW Playing the Pirc also teach you a lot about different structures.