Thank you for replying!
1. I do agree that a two year program will prepare me more for my application, but only under the same circumstances. I have no idea how other factors may influence my PhD application later.
2. I have contacted professors in both programs and they are both willing to let me do research with their group during my MS.
3. I just refer to the astronomy field, considering the information I have got, maybe not so accurate. In Brown there are 3-4 professors doing research concerning astronomy and in NU there are like, 20. I thought it was an important judgement... I really want to get some new and detailed information, though.
4. No scholarships, but I guess one/two years are both fine to me, so I didn't consider financial things.
Some friends asked me to go to NU because they considered its program more competitive and if I fail in applying for PhD this fall, I can still try next year and gap.
Still confused actually... I really have to make up my mind and analyze carefully. I hope I may find a deciding factor and choose without hesitation.
Many thanks for viewing my question and replying!