My republic main is a sage healer. I do well in PVE and PVP. PVP can be hard i suppose because of the cast time heals being interrupted. But once you get comfortable with all your abilities there are work around's. I also find in pvp i do almost equal damage to healing, i find this style of play to be most beneficial to the team. Just keep your bubble and hots on ppl, sprint out of trouble often and cc and knockback when needed. I always pvp with my tank friend. We work very well together and are very hard to kill. PVE is easy mode once you master pvp healing
PS: for pvp having a biochem Reusable medpack combined with your instant cast self heal helps you focus on healing others more as you can heal yourself easy. it also helps you sac hp for force then heal back up quick. plus the rakata stim is nice!