I have a question to add. If say I have a bitcoin wallet that is unencrypted, I make a backup of it and then encrypt the wallet. Years later, I dig up the backup and import it, will the backed up wallet get encrypted aswell or will it be usable and unencrypted?
Not a good idea, if you are using bitcoin-qt. When you encrypt your wallet, it discards all unused keys in the key pool and generates a new batch. Your backup will not have those new keys (usually used for change.)
A good idea is to immediately back up your wallet after you have encrypted it.
A better idea is to create a brand new wallet, encrypt it, and back that one up, then send over all your coins from your old wallet to the new encrypted one that is backed up.
As for blockchain, I have never used it as a wallet. I have only tried bitcoin-qt, electrum, armory, and the android ones (bitcoin for android and bitcoinspinner / mycelium.)
I use QT.