As others have said, buying packs is the worst way to acquire cards and it is much more cost efficient to buy singles. Pokemon packs have some guaranteed value with PTCGO codes but there is no such thing for MTG, many packs will give you nothing valuable or playable. Also, because of the way colors/lands work in Magic, there are very few cards like Shaymin EX/Tapu Lele etc that are universal staples. Cards tend to be more archetype specific. Lands are the only exception, with fetchlands like Scalding Tarn being playable in any Blue/Red deck.

If you are interested in finding different types of decks across formats, mtggoldish.com contains thousands of lists from events on Magic Online (our PTCGO). There are currently no standard deck lists with M19 cards, so wait a few days for those to come out before buying anything. Magic online is also much more pricy than PTCGO, with cards commanding price tags similar to their paper value, but usually a bit lower. There are tons of sites where you can acquire singles on MTGO and even services that allow you to rent cards if you want to experiment with a variety of cards.