it all depends on what career path you want to take. if you want to stay in engineering and perhaps become an engineering manager/director/vp/whatever or if you want to perhaps step outside of engineering into other areas in 'corp america'.
an MS will limit your future career choices compared to an MBA but with an MBA you will not be a subject matter expert in engineering if you wish to stay in engineering.
as far as an online mba, make sure you get it from a program that has a well respected brick-and-mortar counterpart. the degree will not say 'online mba' but recruiters will know it was either a part time or online program when they see you were working while 'attending' school.
if you do wish to change careers outside engineering, the networking/summer internship of a full time mba program are invaluable, not so much if you wish to stay in the same field...