All six of the starter decks are viable decks to play with. They are completely free and you don't have to pay a penny.

The playerbase is relatively small at the moment, so it's likely that you are running into more experienced player regularly. And there is no shame in moving up and down the ranks as you play. Especially if you are trying out new decks. I was Mythic last weekend, Midnight Shadow yesterday, and Solar Gold today.

I made some videos about a month ago playing the starter decks and talking about gameplay strategy. You can see them on YouTube if you're interested.
https://www.youtube.com/channel/UCfc-w4ldqN4Zsa_oNTCnBQA