Huge question, with an equally huge answer. It's like asking what's better - Holden or Ford!
What engine in particular are you talking about? I have seen C O200's go 4000hrs when looked after, and 40hrs when not.
Likewise, a L O230 should easily run for 2500-3000hrs in a C152 or similar small trainer.
Bigger engines, especially turbos may be a little more fragile, however even a properly looked after TIO540 should still have good compressions and make full power right up to the day it is is pulled for overhaul