I'm not a huge Python fan to be honest. The release blurb for the Krait suggested quite strongly it could be used as an alternative to the Python with a smaller capacity but large weapons. Of course it hasn't got the same line up of slots, but how does it compare with firepower?
I have large ships, they're cargo ships, in my mind that's what large ships are for. I like little fighting ships, nimble and manoeuvrable. I like the FAS, it'll take on pretty much anything of it's own size, but it's not strong against anything larger and I need to start working on my combat rep which is woeful!
They have exactly the same firepower 3x large and 2X medium, but you can add an slf or two to the krait to help out.
As for your original question, the core modules, utility slots, and optionals are identical (minus 1 size 6 optional), so the setup costs are pretty much identical. The only differences are the ship cost 50 vs 40 million, and hull costs 135 vs 110? million (Reactive).
The setup costs for both my Python and Krait are around 275 million (before discounts), but that is fully A-rated with Reactive armour - engineering adds no credit cost.
As for which do I prefer flying? Ask me again in a couple of weeks? I love the beefy feel of the Python, and it's a PvE beast when tanked up, but doesn't turn fast enough for some combat. I'm close to finishing the engineering on my Krait and already it feels faster and more agile, it can't match my Python's shield/armour max when kitted for bounty hunting, but with 1000mj and 2200 hull, I expect it to do alright - add in the slf, more ToT, and more evasion... will be testing at the CG.
PS: if you're unsure, buy one, kit it out and fly it... then buy the other and swap all the modules over for a direct comparison.