Holy is fun in BGs. Nothing like hitting power world shield and sprinting away. Cure disease removing poisons on yourself is nice too. Having HW:Sanctuary, lightwell, PoM, CoH, desperate prayer, and stronger renew gives you a lot of spells you can cast/use on the move. Blessed Resilience, guardian spirit are really nice, combined with desperate prayer. Holy Word Chastise is really nice too. Glyphed CoH healing 6 BG players instantly is nice.
Reflective shield is fun in BGs though, watching someone do damage to themselves is always a bonus. Inner focus with strength of soul talent is really nice too. The only "problem" with disc is that they nerfed the duration of pw:s so preshielding a bunch of people in a BG will not only burn your mana but will more than likely be wasted unless they are actively in combat.
Either spec is fun, and both disc and holy you can make one spec that can heal pvp and 5 mans just fine.