The letters of recommendation are supposed to highlight your professional capacity. People who get recommendations from recommenders outside their current company generally do so because they can’t receive a glowing recommendation from a supervisor in their own company.
Thus, if you have two immediate supervisors that can each provide a unique insight into your professional acumen, I would say go with that.
No matter who you choose to write your recommendation letter, you need to be sure of two things before selecting them:
1. They can speak about you in a professional setting and can elaborate on your professional maturity.
2. They understand the value of an MBA for you and are willing to spend the required time writing a good recommendation letter to you.
If the people in your current company seem disinterested in giving you a detailed and well-thought-out recommendation letter, I would suggest asking the Chairwoman of the club you worked for and discern whether she would be able to do the same.
Try to get your current immediate supervisors to write you a glowing recommendation but keep these two conditions in mind as you make the final decision on your recommenders.