Super-speed. Even just being the Flash and living faster than everyone else around you would be torture. It's bad enough just being a normal human fast walker and having to walk behind all these goddamn slow walkers. Then add in the potential to get into accidents easier or even killing innocent bystanders by running through them (as in The Boyz), I'm just not sure super-speed would be worth it, unless it were more like a "time-freezing" ability where you can turn it on and off at will and just walk around doing whatever while everyone else is essentially frozen in place or at a highly reduced speed. Maybe that's even what the Flash's ability actually is, I don't follow the comic at all.