I have made some calculations in Open Beta. From the largest shield with slow regeneration to the smallest one with fastest regeneration the smaler one pays of after 2 mins of fighting. Not calculated are skills or faster rechargerate through more energy into shields. So if you think the fight would take more than 1 or 2 mins then take the regenerative one.
If you have lots of engineering power which gives you lots of shields back in an instant the larger one would seem the better option.
seems like a bugged blue item tbh, they should have 2 quality modifiers on it (the words in the ) but it doesn't so its essentially a white mk 5 compared to a green mk 3.
If your using covariants the green is best, as covariants are primarily used on low shield power settings so you don't really get any regen at all. If you are using high shield settings, covariants really aren't what you should be looking at.
The second shiled has a 25% faster regen.. which is a huge increase... but yes, as already pointed out the first shiled has a capacity bonus, so the actuall total shielding is artifically boosted from the normal