The View Level at AT&T Park features lettered seating rows at the front of the section, a walkway and then numbered rows up a set of stairs. For fans seated in the lettered rows, it's wise to avoid rows A and B to limit the obstruction caused by the railing. For fans considering the numbered rows, there are similar concerns in rows 1-3, especially if you're looking at aisle seats.
Awful Views From Row 1
The photos above serve as extreme examples of how poor the views can be from row 1 in 300-level sections. Kind of ironic that the Giants call this the "View Level", huh? Anyways, the commonality between those photos is two-fold:
1) The seat views were taken sitting down in Row 1
2) The seats were aisle seats
In short, to completely void yourself of a truly embarrassing (the Giants should be embarrassed) sightline, do not sit in aisle seats in rows 1-3. These seats are incredibly tempting because they are just up the stairs and have easy access to the concourse - but the convenience will be over-shadowed by not being able to see the game the way you should.
What Does the Middle of the Row Look Like?
While the middle of the row is not ideal from an access standpoint, it does provide better views when seated in one of the lower rows.