If you are going to Barclays I would want to sit in the lower bowl inside the blue lines. The tickets are pricey, but you'll be assured of nice site lines.
I have sat upstairs in the 200s and found that even if you're seat has an unobstructed view, It's like you are watching ants instead of hockey.
If you have to go upstairs, stay away from the corners.
A quick scan of stubhub show that you will pay at least $130 for decent seats in the lower bowl center (section 125).
Sections 7-9, 23-25 are the best views. 107-109 and 123-125 are also nice. Stay out of the corners and you'll be ok.
Make sure you check out the Koelner BierHalle (KBH). It's not far from Barclays and is an authentic German Bierhall. Good beer and food.
84 St. Marks Pl Brooklyn, NY 11217