Next step up on the trading path would be the Cobra.
For bounty hunting you could try the Viper or Cobra as they can both take pretty much the same weapon/defence loadouts.
For exploring the hauler is actually a decent little ship in it's own right.
I debated about getting the hauler, but in the end I decided, you know what? If I don't try it, I will never know, and will always wonder. So ya, I like it for exploring, and its not so bad for trading either. I once made a profit of 9k from a single trade, and that beats most fedex missions. Plus the added cash from exploring hasn't been too bad. I got interdicted once so far, and I just submitted, dumped all my power into engines, boosted until I could get into supercruise again. Didn't fare too badly.

I guess the trick with a cargo ship is to learn how to run away as fast as possible. Makes for a few tense moments, lol.