The Reman and Romulan sets are Corvarient shields. Best for Cruisers. And the 3 set bonus gives you a Prototype Plasma projectile for the Romulan hyper launcher and a passive ability that boosts shield Cap. Again good for cruisers. For the Defiant the Omega set with tetryon glider and tetryon weps is going to give you the best punch for an escourt. Even without tetryon weps the Omega set is geared toward DPS. Resiliant shields are intended for escourts. Covarient Shild have a very low regen so if you get hit hard you have to use all your heald just to get %50 of you shields back. Where as a resiliant shield you can hit EPS and evasive manuvers get out and your shields will regen fast back up to %100 beacuse of the lower cap. Remember the Defiant is not built for tanking. Its made for hit and run. I actually also have had very, very good results with the Borg XII set on the defiant.