My eng has been doing good with the mirror Voq'uv in pvp and pve, great buy and not to expensive so try it out.
As for the Jem Dreadnought, I don't have or want one but from what I have seen so far people are doing ok in pve with it, but it is failing miserably in pvp. A good eng should be able to tank one person for a long time, but all the people I have seen in this, mostly eng have popped quickly to my Fleet Defiant and Fleet Hoh'sus with no help. Do not use this ship in pvp, or get ready to see the respawn button a lot. This ship should be a priority target as it can do decent damage if left alone, but easy kill and can't escape or heal much.