Over the years when I wasn't running pre-packaged settings from various companies I would run my own homespun settings and genres. What I found was I had what I call "Signature Settings". These are genres and playstyles that sync up nicely with what I'm cozy with running a group on.
For me I had a few Sweet Spots:
Medium/Low Powered Urban Supers - This was just so easy to run. Come up with a reason why powers, dish in conspiracy, maybe some things like rival gangs, TV news, and lots of sneaking around with super powers. I ran SO man games of this using 3rd Edition GURPS, Heroic Tier HERO System in 5th Edition, M&M 2nd Edition, and a bit of D20 Modern when I could. It was cozy really. I loved what you could call post Iron Age, Modern heroic themes. Heroes were people, but still tried to do the right thing. They were NOT supermen, just exceptional and in danger from them selves and others. A lot like White Wolf's attempted Supers game Aberrant. (Which is kinda why I loved that game, if not it's system.)
Actually if you are a fan of TV series like HEROES, Alphas, Arrow, Agents of Shield, even Smallville. This was the kinda game I was running! It was modern enough so I didn't need to explain cultural clues, had powers which made characters interesting, and with a robust enough system I could make rulings on the fly. Good time, good times.
High Magic High Martial Arts Fantasy - Take one part D&D high magic setting, throw them against Wuxia Masters who can cut fireballs with their swords, add a dash of action trumps overplanning, and allow everyone to run around kung fu fighting. I did this setting using GURPS, HERO, and M&M (see a trend?). Supers mechanics worked best for this. Eventually I ran into Exalted which looked like this in a can. Only problem was Exalted (Storyteller 2.0's) mechanics were a carry over from the Trinity line days so had a LOT of issues with defence vs damage, ping, etc. So while I LOVED Exalted setting, mechanically it was a hassle.
There are not as many multi-media examples that match this that don't look like Chanbara or Kung Fu movies from Asia. I guess you could point at stuff like Lord of the Rings, but the power level was way too low. Gandolf made stuff glow and ummm.... Now there were a LOT of 80's cartoons that fit the bill. Pirates of Dark Waters, The Golden Lance, Thundarr the Barbarian, Thundercats, He-man, etc. So there was that.
And those two are my sweet spots. Ultimate comfort, ultimate fun for me as a GM. So how do you find these in yourself?
1. Don't be afraid to make up your own home brew setting using any rule set that works for you. Effect based systems are more friendly to experiment with, but if you can refigure the match on D&D spells to emulate your unique mystic mojo in game. Do it.
2. Go off the rails a lot when thinking up characters. You have to break your limits to know them. Do this in 2-4 session bursts. Then re figure characters and try again at lower power until you find the right 'fit'. This is also how you can come up robust character house rules.
3. Benchmark, Benchmark, Benchmark. You have to find where games break and think of solutions. I found out I liked the high marital arts fantasy when experimenting with GURPS by layering it's FULL magic and FULL marital arts systems together back in the early 90's. And for me, it worked! I had no issues. So down the line I knew I could handle that. I also discovered around the same time I hated world spanning supers games because of the inability to make the PC's feel invested.
A lot of this advice boils down to experimenting and experience. And that is exactly it. Be willing to break the default limits on games, take notes on what works and then try another variant. Over time you'll find you comfort zone. You won't need a pregen setting, just a rule set you like.
Pick up the books, and yammer out the back story to your players as they build characters. Eventually you'll be able to eyeball character gen and do it even faster.
And you will have fun playing in you comfort zone.
Just don't forget to stop, let others run, or try something else for a month or two. Just so you don't get in a GM rut.