My opinion is based on how playable these raid are as balance druid.
1. Heart of Fear (3rd and 4th boss is a nightmare for balance and i really don't like bugs...they are like nazi (Sorry it that offends someone))
2. Dragon Soul (I like the concept, but it was just dull after second or third kill on HC)
3. Every LFR version....Especially second part of Mogushan. "Oh...20 people fell down on elegon...too bad, let's try it again. / "Now only 15 people fell, it's a good progress"