Which area is better for Pursuing a LLM and finding subsequent opportunities?

Probably depends on the speciality. Boston is very good in tax field. Texas (Austin) law school is ranked higher overall.

If your plan is to work where you studied (or in the general area) then it really depends on what you want to do. The market is very different in these places, especially because of the surrounding areas, TX (especially Austin) will be great if you find that there is more for you there, but Boston has the whole New England area and the East Coast generally very accessible.
Ranking are also very important, but overall rankings are just one aspect. You can look at the law schools' rank in the field you want to do, some have a separate LLM ranking, etc.
Also, you may look into the schools' employment rates, which graduates from the school you're looking into are more likely to find a job, is there a difference in employment rates for JD grads or LLM grads, etc.
Faculty is also important, you want connections, those will help you a lot. I don't go to a top ranked law school but have been able to get very good internships because I happened to pick a school with well-known faculty in what I wanted to do.
There are so many ways you can approach this, it's a very personal thing you have to give yourself the time to really see what's important to you, it'll be hard to make a wrong decision if you really cater what the schools have to offer to what you want to do with your careers.

If your plan is to work where you studied (or in the general area) then it really depends on what you want to do. The market is very different in these places, especially because of the surrounding areas, TX (especially Austin) will be great if you find that there is more for you there, but Boston has the whole New England area and the East Coast generally very accessible.
Ranking are also very important, but overall rankings are just one aspect. You can look at the law schools' rank in the field you want to do, some have a separate LLM ranking, etc.
Also, you may look into the schools' employment rates, which graduates from the school you're looking into are more likely to find a job, is there a difference in employment rates for JD grads or LLM grads, etc.
Faculty is also important, you want connections, those will help you a lot. I don't go to a top ranked law school but have been able to get very good internships because I happened to pick a school with well-known faculty in what I wanted to do.
There are so many ways you can approach this, it's a very personal thing you have to give yourself the time to really see what's important to you, it'll be hard to make a wrong decision if you really cater what the schools have to offer to what you want to do with your careers.