Well it is certainly not easy. I've made it to 3 once, 4 twice and 5 three times, but also never made it all the way to legend.
I think Tempo Mage is really strong right now, and not too expensive. And I prefer it without flamewakers.
Then, good old combo druid is still great and not overly expensive, though there are several rares. I've seen a lot of the great streamers climbing and doing well with Druid both last season and now. That would be my suggestion.