It depends a bit. Ifyou have at least to shield healing powers, take shields with a high capacity and redistribute them all the time. If you don't have more than one shield healing power, use something regenerative and move a lot so you are not in focus fire of a tactical escort.
I was told regen shields are not the best and I also heard in game that MACO shield was the best, but I wanted to get the forums opinion on what shields I should use for PVP?
PVP revolves around suviving big alpha strikes, usually from multiple ships, unless you're dueling 1-1. MACO has generally high shield capacities, 5% absorbtion, 10% all-energy damage resistance, and a stacking +2 energy to subsystems proc. when taking enemy weapon fire. However, they only run 150 shield recharge, so they need time to recover after being damaged, even when using shield regen skills like EPtS, Sci-Team, TSS, etc.
Borg shields have the highest regen, but their lower shield capacities make them easy to alpha-strike thru. Omega is a better choice if you want high shield regen since they're only slightly lower capacity than MACO. They don't enjoy MACO's additional absorbtion and resists, but they will work better for hit/run tactics.
MACO's seem to work best on cruisers, while Omega are better on speed-based escorts.