The best card from this event is the attack card (Vanille or Tidus card)from the 6 card pack buyable from shop which is priced at 6 summon card.
The damage once the enemy is in break condition can be up to 30k to 40k. A must card if you want to be attacker in Multiplayer.

Tyro itself is a good card and easily attainable. You also can sell it for 2 abilites card since you can fight in MP without energy if you just join the created game. At least buy one card if hard to decide.

Ifrit card is high in attack power but a little low in break power. So it is suitable for fighting water boss like Shiva during break but if you want to reduce yellow meter, other card is better. The card do can be augmented so it is useful even in future event.

My personal opinion, max it if you can but if can't, at least buy one so you can choose to power up the card later.

For those who just want to started to play, now is the right time with mobius anniversary. Quite a lot give given like free summon once a day, one summon ticket for daily login for 14 days and few more gift.