I just used PDL for a mouse cortical neuron preparation and I found that my cells did not adhere well. I have previous used PLL and found my cells adhere well.
I had this doubt some days back while coating my coverslips, and that time I read this somewhere "Both untreated glass and cells are negatively charged. Poly-lysine is applied to the glass surface to make it positively charged, thereby increasing electrostatic attraction between the glass surface and the cells and thus improving cell attachment. Poly-d-lysine is favored because the d-enantiomer is less prone to protease-mediated breakdown than the naturally-occurring l-enantiomer. Otherwise, Poly-d-Lysine and Poly-l-Lysine are equivalent". Hope this helps!