Small ships: Cobra variants/Viper Mk. IV. <-----These suck enough as it is, anything smaller is hardly worth the time.
Medium ships: Type 6, Asp X, Python (in that order) The T6 is considerably cheaper to outfit, and makes for an excellent budget miner that will actually make you a little money.
Large ships: T7, T9, Clipper, 'Conda, 'Vette, Cutter
I like the Clipper, myself, even though anything with massive cargo space and more internals is generally better. Yes, a T7** and T9 can haul more than a Clipper, but if you're attacked, your odds of survival are considerably lower, you're probably not going to be fighting off much in the big Lakons.
The other big guys can generally hold their own against NPCs.
I've mined in sillier things, but these are generally some of the best. I wouldn't recommend many others.
**The Clipper CAN hold a little more, but I had my mind set on a mining loadout. I'll have to play around with Coriolis to get the real stats here.