Off the top of my head, Vampires, Tanks, Laser Gatlings, Acid Sprayers and N. Weasels have polycrystal bonuses, and I've found Vampires, Gatlings and Weasels to be effective (haven't used tanks or acid sprayers).
The thing about Shield Bearers is they don't really address your problem it seems, because they keep your fighters from dying, but the bombers aren't going to kill your fighters anyway. If you placed your shieldbearers over your tractor turrets, and had enough to capture the entire bomber wave, that should leave you in the clear if you have good success with your shield bearers not dying. Alternatively, just drop the shieldbearers over your command station and you'll have a decent set of extra forcefields.
I also never use riots (I don't think they're effective anymore with some recent changes, but haven't been sure how to quantify it) or raid starships, but I do drop snipers in. Sometimes to deal with raid starships, mostly to just pick off random ships harassing my harvesters.