After I leave active duty in a month, should I get out or serve in the Reserve or Guard?

Join the Guard, they can use your years of training and experience.

If you get out in a month, and you still haven't talked to your Reserve Component Career Counselor, you are late for that required appointment to clear. If you have, go back again. He/she can tell you all the opportunities in the Guard and Reserves within 100 miles of Boston. If you are interested in an MOS change, that needs to be in the contract, as the contract will pinpoint you to a specific MOS/para/line in a unit. most reclass schools in the Guard and Reserves are 4 weeks long and can be straight through or broken up over two annual trainings over two years.
There is no such thing as retraining on a new MOS at a unit.
You will have access to Tricare Reserve Select, the cheapest health plan option anywhere, tuition assistance and student loan repayment. If any of that sounds good to you, then it is worth it.

Reserves don’t have combat arms. The National Guard does. There are two Infantry BNs in MA and also engineers, MPs, Aviation, FA, MI, transportation, etc. Theres also an element from 20th SFG.

Between the states of New England I think most branches of the Army are covered.