subjective question.
What is your goal?
If you want to make sure you get a copy, then standard 1st print is all you need.
If you want to make a quick buck, you (too late) buy the rarer "limited edition or 'variant'" covers as soon as they come out, then re-sell on ebay.
If you are speculating on the book, (too sell later because you think it will continue to grow, or might have its rights bought), then you want to "hoard" a little bit. If you are aggressive, buy some of everything to sell as "groups". If you are conservative, buy two of everything, one to keep and one to sell. Generally speaking, the top variant (sketch in this case) would be the one to buy now, if you think the book has long term potential.
I dont think it has shaken out which will be the second most valuable yet, but Detroit seems to be the leading candidate.
how bout the person that keeps everything...