I've worked as a nursing assistant (hospital), worked with CNAs in a nursing home, and now work in a primary care clinic that hires far more medical assistants than RNs, so I see what the MAs do every day and are responsible for.
As a CNA in a hospital or nursing home you would be responsible for vital signs, physical cares like transfers, toileting, feeding; reporting any changes to the LPN or RN. The training takes much less time. You are probably more likely to get injured. In a hospital setting you would get exposed to more inpatient type of patient population, which could be anything from rehab to ICU or recovery room even. You would work with much more ill/debilitated patients.
MAs do things like vital signs, room patients, assist with pelvic exams, schedule tests and follow up visits. They learn phlebotomy, which is a great skill to have. It takes longer to get certified as an MA because they learn a ton of skills (injections, tympanograms, ear irrigations, just all kinds of things). You might make calls to notify patients of test results, you could get to help with procedures like suturing, abcesses, stuff like that. More chance to work M-F, no holidays, fewer or no weekends depending on when the office is open. As opposed to CNAs, who are needed 24-7-365. Much less lifting and risk of injury as an MA than as a CNA, and patients are pretty much ambulatory and well. You would also work more closely with the docs, NP, PA.
Both positions need good time-management and customer service skills which are essential in health care.
You might want to look at the job availability in your area, what new hires are making for each position, cost of either program in both money and time spent.