I am not sure if there is a `best` cell line. As Cassio said, it depends on what you want to investigate. SK-N-SH and SH-SY5Y are widely used. You can check their properties from ATCC website. They are neuroblastoma cell lines. You can further differentiate SK-N-SH by retinoic acid to express more glutamatergic receptors. Also PC12 cells can be differentiated to have neurites.
Alternatively, you can order neuronal stem cells and differentiate them to neurons before experiment (would be expensive though).
If you need particular characteristics or particular protein (for example you may want cells express X protein), you can always check Protein Atlas (Cell Atlas) database to see which neuronal cells express that protein.