More prestigious how? Because the sponsors say so? The fact the Laureus' voting process is a closed shop of a few dozen academy members, doesn't offer any clarity on its voting nomination process, has for much of its existence shunned football, American sports, cricket, rugby, doesn't suggest to me its any more prestigous than BBC SPOTY.
Unless there's a recognised ranking of sporting awards organisations the task of determining which one is more prestigious is entirely subjective.
In my opinion Laureus is more prestigious than BBC SPOTY and I'm not going to argue with you as to the whys and wherefores of my opinion.