Hmm, let's see.
- Since TNG wasn't an action-oriented series, D got into relatively few scrapes and in those it oft dominated or got dominated quickly. Then there's its obliteration in Generations.
- A wasn't really confronted with long battles either.
- The Defiant survived many battles, some of which proved deadly to might Galaxy-class ships, but it usually did so through alacrity and raw firepower, not resilience.
- Voyager's main trick was its near-endless supply of reset buttons, nothing to do with the ship itself.
- NX sure took a lot of abuse in the Xindi arc.
- E was partly assimilated and used to ram a powerhouse... and live to tell the tale.
So, I'd say: E>NX>Defiant>D>A>Voyager in terms of defensive capability.