I guess it depends on your end goal, cost, pay and what kind of facility you want to work at. Usually when someone becomes an MA that it's their end goal as there really isn't any upward mobility and you can't transition to a nurse. MAs usually only work in clinics as well, I've known a few to work in the hospital but, they're just utilized as a tech or phlebotomist. LPNs have a much larger scope of practice and can work in all areas of healthcare, LTC/SNF, ALF, home health, private duty, corrections, occupational health, insurance, clinics, etc and even some hospitals. Upward mobility is easier for an LPN too, there are LPN to RN transition programs. Depending on your area/state too LPNs can move upward in their place of employment without becoming an RN, they can be charge nurses, unit supervisors and even DONs in ALF facilities. Schooling for MA can be much shorter though if that's a factor for you, in my area it's a 5 month program, 3 days a week and the LPN program is 12 months, 5 days a week. There are also diploma and associate degree (1-2 year) MA programs but, if you're going to go for an associate degree just go for your RN instead. As for pay, LPNs in my area make quite a bit more than MAs, $5-$10 more an hour I'd say. The last time I worked in a clinic, the LPNs made around $5 more per hour. I think it's like that in most areas.
I'd make a pro con list and ask yourself these questions:
What's your end goal?
Do you care about upward mobility or want to be a nurse in the future?
What kind of facility do you want to work in, are you okay with just clinic work or do you want to be able to work in a more wide variety of facilities?
Is school time an option, do you want a quick program or can you devote yourself to a longer one?
Is pay important to you? Pay can vary wildly in different areas.
How important is scope of practice to you?
Look at job postings too, see what is more in demand in your area. In my area LPNs are much more in demand but, I know that's not the case in all areas. Look at job duties and pay if that's included in the job posting.
Also, do a search here on allnurses. These questions pop up from time to time and I'm sure there are some good older threads on the subject.
There are pros and cons to each profession I'm sure. I know there are some comments on older threads where people have been both an MA and an LPN so, those might help you more. Good luck with your decision.