I am not a big expert on this, but I guess you cannot find the Alexa ranking for the subdomains - say Alexa will give rank for hubpages.com but not for softhard.hubpages.com or msivakumar.hubpages.com.
If you review the hubpages.com site within the Alexa you can find out who has more traffic within HP (Click on"detail" button to know more on the traffic). You can find
isabellasnow.hubpages.com getting about .61% traffic (of hubpages) and melbel.hubpages.com getting .31% traffic (of hubpages)
You can get some good insights on the Hubpages.com’s Regional Traffic Ranks also in the Alexa page.