I've been considering the same options as you for next year; a pedestrian/law career can always be defered for a few years, whereas we will only be young, adventurous and eligible simultaneously for a relatively short window.
Personally speaking, I think if I do eventually fully commit to the idea, it would be to aim for Royal Marine Officer. They are fucking bad ass, the training/specialisms on offer is much more down my alley, and maximizes the chance to progress to further bad ass divisions, e.g. The SAS. The elite.
Analyze your personality, research what you would be doing in both career scenarios. As they are so different it shouldn't take you long to realize which you are more suited to/will get the greater satisfaction from.