I have to say, I have pretty much always used the cheapest fuel I can find (as I buy quite a bit of it).
I have also dismantled a few engines in my time, and I have never seen one that is 'gunked up'. Petrol is an excellent cleaning agent, so anything downstream of the fuel entry point is clean save for a bit of staining from the crankcase ventilation system.
If you engine is gunked up, the problem does not lie with the fuel, but a knackered engine.
It also (in my opinion) makes this latest fad for having your engine internally cleaned a complete waste of money! Snake oil. etc.
Chris.