While full Mad Bomber is pretty suicidal good old Mad+Volcanic will leave you with some positive fire resistance, Max CTR and Medium damage. These days it's Mad+Chaos since Chaos is better than Mad in anything but Curse resistance. It's up to you whether you want to craft Chaos since it's better now, or Mad, awaiting the buff that's coming along with Iron Slug getting buffed, stun being completely fixed, Tortodrones returning, and Lockdown getting balanced.

Have you tried consistently bombing without CTR gear? Some find it painful and downright unusable, but if you're okay with it I say go for Mercurial. Your overall damage over time would be less, but it's a very dodgy, safe armour. Mercurial is also the best armour you can get for bombing in Lockdown, as the CTR bonus on other armours wouldn't be wasted there. If you're going to use haze/vortex a lot, on the other hand, definitely go for Volcanic.

Is there a particular reason you don't want a vortex? Not only does it clump together enemies for your party to easily dispatch of, but combined with your Voltaic Tempest you can rack up a ton of elemental damage on the cluster of enemies between the small blast and the spreading shock damage.

For you, I would not recommend shard bombs. Shard bombs need at least Very High damage bonus to become effective, and if you aren't going for UVs, aren't using trinket slots, and don't think you'd go for Mad or Bombtastic, then they'll simply leave you wanting. You could get Scintillating Sun Shards to take advantage of the fiend bonus, but DBB is just generally better and you should start there. You already have DR, and you don't really need a better bomb against slimes than that. The only remaining bomb is Deadly Crystal Bomb, and the damage is simply underwhelming without enough bonuses. Here are options:

-Elemental targets are constructs and undead. You could use DR on constructs and DBB on undead.
-Electron Vortex/Voltaic Tempest/Ash of Agni. Mix and match as preferred.

When choosing a sword or handgun, damage type is the primary consideration. However, when choosing a bomb, damage type is not the primary consideration, for two reasons.

* First, bomb blasts often hit multiple kinds of monsters (e.g. a couple of gremlin menders in a crowd of constructs), making it harder to tune the damage type for the target.

* Second, and more importantly, bombs have highly idiosyncratic effects --- knockback, spreading status, creating a vortex, etc. --- and you often chain these effects together, as in Zeddy's example of shocking a vortex.

So plan around the effects you want, not the damage type you want. This is why any bomber will tell you to get a vortex; it's a totally different effect to add to your toolbox.

You're putting too much stock in Vortex' damage. While adequately damaging, you could use a Graviton Vortex on undead just fine for pretty much the same killspeed.

If you want a normal damage bomb, go ahead and get a blast bomb. Nitro is easy, Irontech is harder to use but somewhat stronger, BAB is the weakest, timewise, but has a ridiculous amount of knockback.