OK so here it goes:
A even number of teath in the sprocket, means every second teath wears down all the time.
A uneven number will make the sprocket last twice as long.
A even number of links in the chain, means the chain is worn only on every second bushing.
A uneven number of links in the chain, means the chain is worn on every bushing.
Longest lasting system is a uneven sprocket, inside a uneven chain