I am an MA working towards becoming an RN. I would recommend that you go straight for RN, but if that's not an option, LVN would be best.
First, LVNs advance more easily. There are more options available and it is possible to get in a fast track to RN program.
Also the pay is better. Depending on where you work, you may or may not have the same duties as an LVN, but the pay is going to be low. I have worked at a large clinic where LVNs, MAs, and an RN worked. At that place, the nurses got the nicer job descriptions and more money. I have also worked at a small clinic where only MAs were employed and we did everything. I got a lot of experience, but still was paid as an MA. Now, I work at a hospital as a PCT. There are very few LVNs there, as they are being phased out at many hospitals. However, there is one on my floor, and she is a nurse with a few limitations in what she is allowed to do, and I am a tech.
Furthermore, if you think that the market is flooded with nurses, the situation is far worse for MAs. As far as I know, only 2 other MAs in my class are working in the medical field at all! It's not just my class, either. At the small clinic I worked in, we always had MA externs around. When they graduated, they generally didn't get jobs. These vocational schools churn out as many MAs as they can, charging more money than many nursing programs, while lying about what a shortage there is, how you will be able to work anywhere, and how great the money will be. Because it's such a short program, a lot of people are drawn to it
Sorry this has been such a long post, but I feel strongly about the topic.
If you want a quality education, go for a nursing degree. Usually your MA courses don't transfer anywhere, so if you want a nursing degree later, you start from scratch. Your opportunities as an MA are usually limited to doctor's offices. I was lucky to get a hospital job. MAs aren't really trained for that. Also, while MAs can be perfectly intelligent people, you just don't learn the assessment and critical thinking skills that you get in nursing school. I have heard some pretty scary things said to patients by MAs over the years. Not because they are dumb, but because they are often encouraged by the doctors employing them to basically be nurses for rock-bottom prices, and an MA program doesn't prepare you for that. It's just not fair to you, the patients, or the more qualified people who could do the job.