I faced a similar quandary when I made the jump from my trusty Cobra Mk III. I thought the Krait was probably the better multipurpose ship, but the Python's extra cargo carrying capacity would allow me to make money lugging cargo faster. I was tempted by both, but could only afford one.
In the end I was leaning towards the Krait but wanted to give the Python a fair chance to change my mind before I started upgrading, so I bought one to try out the handling and experience the more enclosed cockpit. I took it out of the station, pulled back on the stick and waited... After the Cobra it felt like I was flying through treacle and the view from the cockpit was far too limiting for my tastes. I flew straight back in to the station and sold it, then headed off to buy the Krait. The differences in visibility and handling were much more than the stats would suggest. The 10% hit in credits (Li Yong-Rui system so less than it could have been) I swallowed to test out the Python was money well spent as I was sure about my decision and could throw all my energy and credits into upgrading the Krait.
I understand the appeal of the Python if you are going to be lugging canisters around the galaxy and generally not seeking out combat; it is a superior workhorse. For me at least the Krait is just more fun to fly and fight, more flexible in terms of it's role and a swift loadout change transforms it into anything I want. Don't underestimate the impact of the SLF either; a GELID F beam laser equipped fighter with an experienced pilot is a force-multiplier, particularly against NPCs, who seem mesmerised by the tiny little insect buzzing around them melting their shields. I just wish Frontier would listen to their player-base and let my crewmember sit in my cockpit; it's so tiresome having to get up and fetch my own coffee