Well unless you put in a really expensive race car engine in your car, 93-octane won't make any difference.
For your Corolla, if your engine pings a lot, i'd say maybe go with 89 but... yah 87 should be fine.
I think the difference between the octanes is that hte higher ones supposedly burn at a slightly higher temperature (someone correct me if i'm wrong). And b/c the Toyota Corolla's engine is set for 87 octane, you won't see any benefits by going to a higher octane. Just more money out of your pocket.