Restoration Druids are considered by many to be the best healer for PvP in TBC, and for very good reason. The majority of their healing comes from HoTs like Lifebloom and Rejuvenation, meaning you're not required to constantly cast to heal through damage - making interrupts far less of a problem. Combined with Swiftmend and Nature's Swiftness for emergency direct heals, you have incredible flexibility.
Healing wise, Druid is quite simple - all of your healing is instant. But that's not what Druid is about. At its core, Druid has a ton of depth. You're required to keep your team aggressive, reduce damage with crowd control, set up kills, kite enemies, and control the pace of the game - all while keeping your team alive. Having all of these tools that you're expected to use in arena can be very daunting.
✓ Strengths
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HoT-based healing lets you keep moving and avoid interrupts
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Cyclone is one of the strongest CC abilities in the game - 6 second lockout, can't be healed, damaged, or deal damage
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Multiple forms of crowd control (Cyclone, Bash, Entangling Roots, Hibernate, Maim, Pounce)
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Shapeshifting removes roots and snares, provides mobility and survivability
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One of the only healers with an interrupt
✕ Weaknesses
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Cannot dispel magic effects - only poison and curses
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High skill ceiling with many tools to manage simultaneously
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Lower direct damage compared to other healers