So, the obvious choice is to not mess with time nor life.
To humor the idea of picking the age I'd live to; I'd probably choose to live up to about 986 years, or to year 3001.
A more realistic choice would be to cut my body's aging rate (can I do that) to 1/3 and live 150 years to physically age to 50.
as for the infinity bros? No thank you, I'll gladly die.