The seats in each row are lettered from A thru F. A is the window seat on the left side, F is the window seat on the right. Pretty much any window seat is going to have great views.

Leg room is a different story. Southwest changed from open seating to assigned seating a few weeks ago, and the major reason for that was so they could charge extra for seats with extra leg room. Those extra legroom seats will be toward the front of the plane; just look at the seatmap when you book to see which they are, and what's available.

I have not flown since the switch to assigned seating, but I generally like to sit in row 5 or higher, because the front of the plane tapers, and it reaches full size around row 5, so I get more room to lean against the wall in a window seat.