This is a very personalized decision to your circumstances. You also aren't clear what your decision is.
1. Are you just getting out of undergraduate and wondering if you should go on to graduate school (JD/MBA)?
2. Are you admitted to an MBA program and trying to decide if you want to get a joint JD/MBA?
3. Are you admitted to a JD program and trying to decide if you want to get a joint JD/MBA?
4. Something else I can't imagine right now?
Personally, I am not a believer in the joint programs. I say you do one or the other. Unless you are going for a fairly specialized position, there isn't much benefit from doing both. You spend an extra year in school, but don't typically get any extra salary. Now, there are some jobs that may seek out JD/MBAs. You may also not care about working and earning money, and just want to experience school. For 99% of the people, I'd recommend sticking to just one program, though.