How to choose between PhD projects?

I am trying to decide which project would be more worthwhile to spend my years on, in terms of publications, novel research and contribution towards my thesis defense. I am just into my second semester with my adviser, who has assigned me and another student to collaborate on a project, that is interesting and does seem to have good potential in my field. I also have the opportunity to work on a related project within my research group at work, though it might involve legal agreements for my adviser to be involved and limited/no funding. My adviser seems to be fine with my involvement as long as it is related to his research interests. My intention of pursuing the research topic at work, is that I can overlap both my work hours and research hours (my employer is sponsoring my PhD). It seems that I can either choose to work on my adviser's project or my employer's project with my adviser's blessing. The question is which one ? Any thoughts or advise on what should I consider in this case ?