When the enemy is dumping on you, shield capacity is what keeps your hull intact. The bigger the shield volume, the better.
The downside is it takes longer for big shields to fully restore. You will be running around with 3/4 shields a lot more often. Uncharged shields dont help you with part A above. You can overcome this by increasing regeneration rate. Try to find a Positron Deflector with [Em] and [ShdS] values, they will improve your shield performance a bit. The Aegis deflector is better if you can do it, and the Omega rewards are better still.
I always used high capacity shields but was recently pointed towards lower capacity highly regenerative ones. It's working great for me in eSTFs. They usually re-build by themselves but I can hit TSS2 and an aux battery in combat if I'm stuck. If I'm in real trouble, I will will run and repair. The repair is so quick I am back in no time, which wasn't the case when I used the MACO.
I would recommend the Assimilated or Omega Shield. Which you go for will mainly depend on set bonuses.
You can get a regenerative Shield Mk XII [Cap][Pla][Reg] for about 500K EC on the exchange which will let you experiment as it gives most of the benefits of the above shields without spending DL or marks.
I'll post everything I'm running when get the chance 2 sign into game again, I do have all set up suited for me it's just the fact I can not last long with direct hits and its driving me nuts as I feel like I'm always running or dying lol