There is no guaranteed acceptance with either program. They both abide by the same articulation agreement, which will grant you an interview at both campuses for various programs (Pharm, Dent, DO, Opt, PT, PA, etc.) for two cycles (the cycle you start the program in and the year after) if you meet minimum standards for applying to the program (found on the program specific web pages on Midwestern's website), maintain a 3.0+ GPA for the first two quarters (it might be first year for the two year program, I'm not entirely sure), have a test score for the program within one standard deviation of the program average from the year before (for AZCOM, the average MCAT the year before was a 508, so to qualify this year you needed a 506+) and stay on track to graduate/complete the program.
From firsthand experience, getting into the med program is a lot harder because the school doesn't save seats for Masters students and the class is pretty full by the time you qualify for the interview. However, Dental students have the benefit of having seats reserved for them, and you can get in as long as you have a decent DAT and can keep around a 3.2/3.3 for the program. Most people from my program that were pre-dental got in to one (or both) of the dental programs at Midwestern.
I would only recommend the two year track if you really need help on your app with extracurriculars, to significantly patch your GPA or if you need to retake your tests. If you are just missing one piece (besides the test score) to get you to the interview, do the MABS program. If you really need to boost your application with research, recommendations, or extracurriculars along with your GPA/Test, I'd go with the two year program.