I would skip the flash and go with functional and durable. Some kids in our neighborhood got the kind with the sparks and it wasn't long before I saw the spark maker piece lying on the curb, either broken, broken off, or worn out. (the sparks are created by friction between some flinty piece and the asphalt when they ride).
In my opinion, it is just another part to need replacing and the kids can't really see it when they are riding anyway. If they can, then it's a distraction from what they SHOULD be paying attention to (what's in front of them).
Outside of that... get whatever brand. But avoid the pump ones. Both our kids had those. Son's was very heavy duty, and it was hard to pump the leg device. Daughter's was much easier (and smaller) but, well, something on it must've broken b/c I don't even know where it is or what happened to it anymore. Our kids got electric scooters when they got to ages 12 and 10.