It differs from person to person what you will consider more difficult.
For example, I consider Erudax in Grim Batol and Setesh in Halls of Origination to be the two easiest boss fights in heroic to heal when done correctly... because I've done both without a healer. Erudax all damage except direct melee damage on the tank is avoidable and direct damage on the tank can be so trivial the tank can heal themselves. Setesh is similar, in order to reduce the amount of damage you take by a ton, you do more DPS (portals die faster, less adds, less damage taken, more damage on the boss). The tank can take care of themselves for a very long time before they are overrun. These types of experiences are not the same for everyone.
"In anything, if you want to go from just a beginner to a pro, you need a montage." /w TankSpot WTB Montage for Raiders.