Let's put it this way... with PPS (f2pool) you absolutely can NEVER make above expectations because of the way the payout scheme works.  With PPLNS (kano.is, p2pool, etc) you have the POSSIBILITY of making more than expectations.  You also have the POSSIBILITY of making less.

PPS puts all risk on the pool operator, because miners will get paid for submitted shares regardless of whether or not the pool finds a block.  That's why any PPS pool charges fees - to help mitigate some of that risk.

PPLNS transfers risk to miners.  You are only paid for N shares, regardless of how long it took the pool to find a block.