Arena-feral druids not best at it , more of a balance resto thing.
battlegrounds- doesnt really matter id go feral or balance for bg's
raiding - if u want to be the OT then be feral if you want to dps go balance
heroic/normal - your going to be expected to tank if feral but also moonkins arent the most wanted in heroic/normal groups ... resto is always wanted in dungeons
Most will want to use a point in Nature's Grasp to help with getting away, but this is the set-up I've found works best for my play style. I use the exact same set-up for Battlegrounds. If you want to switch to pve, then you need to go hit the trainer and respec, unless you're simply doing DPS in cat, you'll be fine for the most part, but I would still probably go respec to max out Predatory Instincts.
My PVE set-up is usually like this so that I can tank and DPS in the same spec: