Krait mk.II
You can't look at the stock hull cost as neither of these two is usable stock. A decently equipped Python will cost you 200 million. Anything less and it's a death trap that can't jump, fly, or run. T9 about 150 million.
Both ships are as un-fun to fly as it gets, but at least in case of T9 it's understandable because it can haul four times as much cargo.
And don't forget T7. More cargo than Python, more agile, better armour,... The only downside is that it can't land on outpost, like T9 (requires large landing pad)
Krait is much more fun to fly, has better jump range, is faster than all the others and costs half. It hauls the least amount of cargo, though. So it really boils down to what you want to do.
Mission, long range hauls or passengers - Krait
Pure bulk trading and stacking of delivery missions - T9
Or even better. Go here:
https://coriolis.edcd.io/
and build one of each ship the way you plan to use them and compare the cargo, jump ranges, speeds and prices, then decide.