The third base side of Petco Park will get the shade first and have the sun behind them during late afternoon and evening games. Seats at the top rows of Section 110 will have very good shade for most of the game, but you may have to turn your head quite a bit to the left to get a good view of the scoreboard located above the left field wall. Your view of the scoreboard won't be obstructed, but from that angle and with the seats facing the pitchers mound, it just requires a bit of effort the see it.

View of outfield from Section 110 at PETCO Park
This is the view of the outfield from Section 110 of PETCO Park, the scoreboard can be seen on the left edge of the image.