How do I know I'm choosing the best card in the keg?

In Gwent, when you open a Keg you get to choose which rare you get among three different cards.

If I'm not aiming for a particular deck (or if none of the cards I get are in that decklist) how do I know which cards I'd better get? I'm not an experienced player, I've seen a few decks and I have no idea if they're strong or if I just played badly against their startegy so I have no idea which cards are good, or if there are ostensibly bad ones I should avoid.

I'd like this decision to prove valid at least for the current meta.