Well, as I've yet to be able to afford any big ships....
Let me see, I've had my Cobra pretty much since week one. I love it. Super fast, very flexible. Good in combat, good for trading, good for exploring. Don't have to think about it, just take it and go do what you want. I ran rares with it, bounty hunted, farmed CZ's, explored the fringes of the bubble, did some ranking up. Just get in and GO. I'm looking forward to the MkIV - could be a fantastic long-range gunship.
In the past I've tried eagles and vipers but really didn't like them. The eagle is made of paper and small hardpoints are a joke; I just didn't like the viper much.
I've recently upgraded to a t6 for trading, and have forgone popping pirates when they try to pull me down for time. She's a sturdy ship, lots of capacity. Surprisingly fast.
Even more recently, I started farming PowerPlay merits, trying to get up to rank 5 so that I might have a chance at piloting a big ship sometime this decade.
For this I blew nearly all my money on a $20Mil Vulture build.
Slow. Agile enough though, but very slow. The jump range is crap compared to what I'm used to with my Cobra and t6. Did I mention it's slow?
But god DAMN is it good at blowing s**t up. And those shields just last forever. I'm having a lot of fun with it, despite the sluggishness. (D4 thrusters).