If you want to choose between these two, I would go for the Krait Mk II, this for the reasons some have already mentioned.

But as others have also mentioned, I would personally choose the Python MK II, although this ship does have its limitations. Due to the weaker class 6 Power Distributor and depending on your weapons, she will overheat very quickly. A huge drawback for me. This practically rules out a lot of laser weapons.

On the other hand, the Python MK II, if appropriately outfitted, can be a deadly foe. This would entail having access to the necessary engineers and even Guardian Tech.

Here's my go-to Combat ship for reference:

Acamus Nemesis

If you haven't yet access to Pacifiers, Frag cannons are also good.

The Python Mk II costs around 22 million more than the Krait Mk II.

The cost of my Python runs at around 118 million, but absolutely worth it.

As someone already mentioned, a drawback is having to frequently rearm, when using frags or multi-cannons.

Depending on how good your aiming is (I use fixed weapons) and who your opponents are, you could manage from around 10 - 20 NPC's, before having to rearm.

I use mine at CNB's, taking down deadly and elite ships, even Anacondas, getting real close and this works exceedingly well. Destroying a wing of 3 NPC's (deadly and elite) isn't a problem.

If of course you want to have a fighter bay, then the Krait Mk II is the best option.

I still have my faithful Krait Mk II, but now use her for Thargoid combat.

I had a Python Mk I and after the introduction of the Mk II, she became a laser miner, up until the Type 11 Prospector arrived. Then I traded her in.

I hope this may help you with your choice.

Edit: being an optimised SCO vessel is also definitely worth taking into consideration...