It would depend on where you are pinging from and if they have anything closer to you to respond.

From where I am, google averages 4ms, yahoo is at 200ms+. Obviously because they dont have the money or marketshare to bother putting anything for me to route closer too.

Same experiment from my gigabit link in Silicon Valley. Looks like Yahoo is about 3 times slower but far more consistent

--- google.com ping statistics ---

20 packets transmitted, 20 packets received, 0.0% packet loss

round-trip min/avg/max/stddev = 6.918/23.419/294.037/62.272 ms

--- yahoo.com ping statistics ---

20 packets transmitted, 20 packets received, 0.0% packet loss

round-trip min/avg/max/stddev = 78.056/78.940/80.940/0.811 ms

Although what's interesting is that Yahoo is really more like 10 times slower (almost every ping was in the 6-8ms range), it's just that there was just that one packet at 300ms and other at 30ms that really blew out the average.