War of the Spark is an incredible set. I'm writing this on the eve of Mythic Championship II in London, where I'll be drafting War of the Spark in the highest-stakes Prerelease there ever has been. That's really cool, and a big part of that is how fun this set is. It's a format defined by planeswalkers, and as such, you really need to get on the board quickly and have good tools to battle opposing 'walkers. WAR also has one of the highest densities of great cards we've seen in a while, as you'll soon see from the breakdown below.
I've divided the set into four categories, though, given that I left many cards off (cards you would basically never first pick), there's really a fifth category: unlisted. The other four categories will go in descending order, from the cards you slam every time, to good rares and the best uncommons, to good uncommons and the best commons, and finally the good commons (with some overlap between rarities in all groups, based on power level). All lists are in rough order, starting from the best cards in the group and going toward the bottom.
Let's get to it!
The Best of the Best
These are the cards you hope to see when you crack a pack, and there are more on this list than any set in recent memory. This is a high-power format, and there will be a lot of awesome cards floating around. The best cards are a collection of planeswalkers, God-Eternals, Finales, and otherwise busted rares. If you see these, take them, and it's worth switching colors much of the time if you encounter one later in the draft.
The Best of the Rest
If you open a card on this list, you're still doing quite well for yourself. In fact, many cards on this list would be close to the top in any other set, but in War of the Spark, there is some stiff competition. The hybrid planeswalkers are so high up the list because they are flexible; taking one doesn't commit you to any specific color, which is very powerful.
A Good Start
Here we have a collection of good cards that you're always excited to have in your deck, even if you'd rather not start with one. Kicking things off with one of the best commons or a good uncommon isn't bad, but in this set, you will always feel like you can do better.
I'd rather not start with one of these, as decent commons and uncommons are cards you'd rather be taking mid-pack, not first pick. Still, a good amount of the time, you will end up selecting one of these cards, and there's no shame in doing so.
This format is a ton of fun, and I can't wait to dive into it. Good luck in your drafts, and don't let your opponents harvest your Spark!