I want to get into a tcg. Which do you suggest? Is online viable?

Magic the Gathering has Cockatrice and a few other free clients. The official one is balls and might get replaced soon.
Yu-Gi-Oh has a free online client and got an official one not too long ago.
Pokémon has an official client that's well supported and probably a few free ones somewhere.

That's the big three. Official ones always means a certain amount of "Either pay or play a stupid amount of time to win".
Disregard Hearthstone, it's a complete shitfest and everyone playing it hates it.

>>51987340
As far as paper goes, you should pick one that you'll have people to play with. Getting into a card game with nobody to play with defeats the entire purpose. Check out your local game shop and see what's being played before buying any physical cards.

Online is definitely viable. Magic The Gathering Online has been around for over a decade and it's only getting better (though it's horribly dated by today's standards). It's only barrier is the entry cost, a flat $10 sign up fee and then more money for whatever kind of deck you want to build.

Hearthstone is free to play with daily quests that reward in-game money to buy booster packs (5 card boosters are $2.99) and has the best UI you'll see out of them all, it's smooth and slick and easy to play but it's metagame is fucking miserable right now.

Shadowverse is another free one and it's popular among weebs but it's longevity is questionable and it's aesthetic doesn't appeal to me personally.

Yugioh has a smartphone app game that's not so bad or so I've heard.
Pokemon Online has the neat gimmick of letting you redeem paper cards online, otherwise you play for cards like Hearthstone.

Also Magic has a few unofficial, third party clients floating around that let you play online entirely for free like Xmage and Cockatrice that are pretty neato. Xmage is a lot like Magic Online and Cockatrice is entirely manual, so you really need to know the people you're playing with or expect cheating to occur.

Ignore everything that's a mtg or hearthstone clone.

Just start with Pokemon and then move on to the next

>>51987340
Star Wars: CCG by Decipher.