Double the pay definitely! I don't have to make any changes to what I normally do so I'd still have the same schedule and same amount of spare time, which I have loads of already sooooo, then I can keep saving more and more. (If I was living comfortably with my regular pay, then I would probably just put the extra into savings for the future). It means that I will always have money to fall back on, savings for emergencies, etc, so I would never have to take out a loan if something were to break or whatever meaning that I won't go into debt!
Thinking about it, they're the same. If you work your usual time with the 1st option, that's normal time, twice the pay. Reverse for the second option and it's equal to the first one. But uhh half the hours same pay.