Echo most other comments: Exit row gives more space (choose the most rear if there are two) and almost always has an empty middle seat. Econ Comfort gets you nearer the front but is often fuller. Which of those 2 you prefer is your choice. I almost always choose the Exit Row.

BTW: on my most recent -700 the Exit Row config had changed. Now only one real Exit seat near the window with a missing seat in the row in front. The B, C, D, and E seats were regular. This is definitely not a good arrangement, as well as nothing on the floor there is also no seat pocket or tray table within reach. Also not possible to sit 2 together with this arrangement.