Scan the QR Codes in the links above. Make sure you have the O-Power for experience and Lucky Eggs. The secret bases above will have trainers that uses 3 Blisseys. They are, by far, the fasted method I've found -- aside from Rare Candies. They only have Healing Wish as their skill so you don't have to do much -- they'll kill themselves for you.
Note 1: Make sure you use the level release to get maximum experience points.
Note 2: To get the most out of them, battle them in their base then recruit them to be one of your grunts. Go back to you base then battle them again. After that, just remove them as your grunts and repeat the whole process tomorrow.
Note 3: I think the maximum favorites you can have is 15.
Note 4: If adding them gives you an error that says something like "you already have a friend who uses that spot", you can either delete that secret base or find a different QR Code.
Note 5: You can only battle the trainers 1 day after adding them.