SpideroakUbuntu OneDropboxSkyDrive Synced StorageiDriveSyncLiveKive (AVG)
Free Storage2GB2Gb2Gb/8GB**5GB5GB5GB
Additional Storage Costs100GB/$10020GB/$29.9950GB/$99 100GB/$199Unlim/$59.8825GB/$49.99 Unlim/$79.99
PC ClientYesYes(Beta)YesYesYesYes
Linux ClientYesYesYesNoNoNo
Mac ClientYesNoYesYesYesYes
Android ClientYesYes*YesNoNoYes
iPhone ClientYesYes*YesNoNoYes

I personally go with Dropbox as I find the client to be small and pretty unobtrusive. But I’ve not used the others intensively.  I’ll leave you to have a try and there is 21GB or more to play with!