I'd say that "Just Plain Lucky" is probably the hardest. It's something you just sorta have to wait for and with only 1 chance in a million of getting it, it's about 138 hours of having the game online to get it.
Four leaf is a bit easy you need essence of redoubled luck heavenly upgrade wait for the lucky 2 golden cookies to spawn have enough magic for force the magic hand of fate and refill with a lump and force the magic hand of face