I'm using 1 Password on my iMac to store my passwords. In order to sync 1 Password w/my iPhone and iPad I can use Dropbox or iCloud -- I can't use Wi-Fi to sync both primary and secondary vaults in 1 Password. Which is more secure, Dropbox or iCloud?
The security details for both Dropbox and iCloud are similar. Both encrypt data on the servers, both encrypt data in transit.
Where things may diverge is a) functionality and b) privacy. It should be noted that 1Password on Dropbox offers a web interface into your password vault; if Dropbox is violated, then your vault can be accessed if someone has your password. However, having the web interface can be a boon to users who want to temporarily access the vault without installing the software.
Privacy is an effort best left to the readers. Apple's US Privacy Policy and Dropbox's Privacy Policy.
Is there not the same risk if iCloud were violated, and had the password for my vault?
Not exactly. The point I was trying to make is that the web interface to your Vault is accessible via the web interface to Dropbox and the JavaScript engine that Agile has built for 1Password; those interfaces are not available in iCloud, at least not in the current version. You cannot access your files via the web interface to iCloud; ergo, you cannot access your Vault via a web interface.
This is an odd cousin to "security through obscurity" -- security through a lack of a feature. You lose a bit of insecurity, but you also lose functionality.
Compare and contrast security on Dropbox and iCloud
