This is even more difficult when you don't even have your collection of old cards well defined with optimal levels. However, I have used these statistics to know which cards to raise and which to sell based on their performance and their market price and I have remained solid in the diamond league when previously I could not exceed gold I.
The cube and the kraken are rewards cards and are increasingly used, especially the cube. the Failed Summoner seems to work very well, although for me it is very expensive but if its price is not a problem it is an excellent card. I had not paid much attention to the Vigilator but it also seems to do its job.
I pulled a gold foil failed summoner, then checked the peakmonsters bulk feature, and found a couple more gold foils going cheap :)
That's very nice, sometimes some cards are cheaper when they're gold. Market stuff.