The lower one, if you want your tubes to last. The higher one, if you want the amp to perform to design spec.
Tube bias is an ever-shifting target. In the majority of amps where bias is fixed the designer/manufacturer has been forced to choose a bias that will deliver whatever power and tube life they are going for. The tradeoff is higher power/lower tube life. The main tradeoff, not the only one. Amps like Prima Luna can get around this with active bias, but this is not easily (read, expensively) implemented.
Tube bias is an ever-shifting target. In the majority of amps where bias is fixed the designer/manufacturer has been forced to choose a bias that will deliver whatever power and tube life they are going for. The tradeoff is higher power/lower tube life. The main tradeoff, not the only one. Amps like Prima Luna can get around this with active bias, but this is not easily (read, expensively) implemented.