I find that I keep returning to the Cobra. If I'm starting from a clean save, my first milestone is to get into a Cobra. I flew an Asp for a little while, and it's a very nice ship, but I end up missing the speed. That, and the Asp is an enormous ship. I prefer the compact feeling of the Cobra. I've flown T6s, Vultures, etc., and I still prefer my Cobra. Oddly, it never used to be a favorite of mine. The hardpoint placement is pretty wonky, and it could really benefit from another utility hardpoint or two. The shields are weak, and while the hull is decently strong, once those shields drop, it's time to scoot. Luckily, nothing scoots better. The ship has really grown on me, as I've flown it more and more.
I took a page from another CMDR and outfitted mine for pure speed. 315 cruise with four pips to engines, and 452 boost, with a hair over 20ly laden range. With 40t of cargo space, she'll make a good smuggler or rares trader, if I ever get around to doing either. The Cobra is kind of an 'end game' ship for me. There are objectively better ships, of course, but subjectively I haven't flown another that feels quite as well put together, all factors considered. I'm hoping the Diamondback evokes similar feelings...
Good luck in your search, Commander.