Midwood Street is the most expensive and best street in the neighborhood. Maple Street is competitive with Midwood Street and has freestanding homes (whereas Midwood Street is all rowhouses, though some are semi-detached), which some prefer. Generally, anywhere on Lefferts Manor, the area with the one-family covenant in their deeds, is the best part of PLG. The Manor includes Midwood, Maple and Rutland between Flatbush and Rogers and also includes parts of Lincoln Road and Fenimore Street in those blocks, as well as a tail up to Lefferts Avenue and Sterling Street from Bedford over to Nostrand. (The map below shows the Manor.)
Of course, if you're looking for apartments, you're not looking on the Manor. But then I would look immediately adjacent to the Manor, along the parts of Fenimore Street and Lincoln Road that are not part of the Manor but face the Manor across the street (i.e., the south side of Fenimore between Rogers and Flatbush or the north side of Lincoln between Bedford and Flatbush).
Generally speaking, the closer to the Manor, the better. East of Rogers, the neighborhood goes downhill pretty rapidly, especially around and east of Nostrand, and south of Fenimore it also declines fairly quickly. I wouldn't consider Lenox Road PLG at all--I think PLG ends at Parkside Avenue.