It really depends. What do you normally fly? Do you like hunters and their flight style? What about invokers? Do you need something less skill intensive like a warrior/sorcerer?
I know many are putting down both mythics this season, but let’s be real. It is only the start of week 2. We have no idea how fliers will feel about these mythics come week 8 when more people have one and have had time to fly them for themselves. The same things were said about Lockjaw and Quasar. They ended up being really good mythic warriors.
Another fact to consider, just because the “community” goes ga ga over a hunter, doesn’t mean YOU will like the hunter. So many people absolutely loved Calavore, took me 2 months to learn to fly him. I am the same with Jaalkan. So really, YOU need to know YOUR skill ability first. If you don’t like hunters, well then you might find that the “community adored” hunter is just not your style, and that is okay. Take all these “community opinions” (even mine) with a heap of salt and realize that they mean diddly squat if all the popular opinions are for flight styles you don’t enjoy.
With all that said, if you do NOT have a mythic yet and you are not trying to hitting level 550+ bases triple defended all day, the warrior is a good starting mythic to have. You need really good skills, maybe even better than hunter skills, to fly Steelwing defended so I would not recommend him for someone without another mythic as backup.
If you absolutely love invokers, especially like Jinn and Ikkuma, then you will really like Steelwing.
Edit: To know whether you can get a mythic for your situation, your team, how much you can push, etc. Go get a copy of the Season planner from the Spreadsheet Vault and fill it out. It really will show you whether you can get the sigils required in the 13 weeks to get a mythic or not for your activity level. If you can’t without going beyond your limits, then just open what you need to do events and save for next season.