Interesting question and a tough choice too. Having a lot of money from the lottery would give me complete independence, yes, but after one has spent and invested, and given to some charities, there's not much else to do except simply building up that money. However, with very little deliberation (lol) I would rather be President for a variety of reasons.
As President, I would probably get a lottery size salary anyway, with lots of income for public speaking and writing books after my term was over. I would not be short of money, neither in the post or when I leave it.
My day would be very varied as I wouldn't know what was going to call my attention next. I could look forward to a very challenging life!
I would have the authority to make decisions that can have real impact on my country.
Above all, I would have the power to influence an awful lot of things in the country, especially on a positive level, and be able to leave a kind of legacy when I go.