I personally fly the Python. I'd say if you can afford it, get a Python. If not, get a Clipper...
until you can afford a Python...
The Python flies very similarly to a Viper. I'd actually almost call it a Medium-sized Viper... with huge fangs. It has a lot of mass as well, so it rams nicely too.

You can outfit the Python to have 268 Cargo and still have a Shield, Shield Bank, and Fuel Scoop. The fuel scoop is ESSENTIAL on the Python, since the costs are about 3k per 1% of fuel. The Python also has hardpoints that are very close together, and so Fixed weapons are easily do-able if that's your preference. Since it's Medium, it can also land at Outposts, something the other two can't do. The pitch on the Python is great, but the yaw is fairly cruddy. You'll be doing a lot of rolling to get on target.
Python also costs way more than the other two, though. Don't scratch it, it's costly. If you have the money, Python all the way!
If you want a Python, wait until you have at very MINIMUM 70-75 mil for upgrades and insurance (which is easily over the 3 mil mark with a few simple upgrades).