Comfort. That's the single most important measure of a bike and a rider's compatibility.
If you have a bike frame that is too big or small, too long or short, it will exhibit as aches and pains from riding. You won't want to ride a bike that hurts.
How to measure "comfort" ? You as the rider have to get on the bike and try it out. Being younger, you can probably adapt yourself more than a less-flexible rider (ie older person.)
Normally, a moment on the bike can be enough to categorically say "no I don't like this" A short ride around a carpark or around the block might give you some ideas. A proper ride would be 30-60 minutes, and involve some road, and short climb and short descent, and some turns and low-speed manoevers. If you're looking to stunt the bike, then ideally you want to try some jumps and so on.
Few new-bike sellers will let you go for a long cruise though, so one solution is to look out for demo-days. Locally a brand might tour with a trailer full of new model bikes for test rides, Giant do this annually. Downside, they're generally the very top models and demoing electric MTBs and so on, which will be outside your budget.
If buying second-hand, a seller who is a rider may come with you for a test ride. That can be an awesome way to find new riding partners too.
Given your age, you are still growing so any bike that fits now, may not fit as well in a couple years, so consider resale value. That means don't strip the decals and don't give it a rubbish paint job. If you do, take photos of it before making changes.
The technical specs of your bike don't really matter. As long as it is safe, and goes and stops as expected, the number of gears and teeth and angles don't make a lot of difference other than "this bike feels different to that bike" so you have to ride them to compare.
Good luck with your searching.