I really can't decide which is the best dev. I will just list my favorite dev.
Atlus- because of Shin megami Tensei especially Persona
Level 5
NaughtyDog- Uncharted
Sega- Yakuza, VC
Konami- Developers of Suikoden and Team Silent? Kojima Productions
Team ICO
Tri-Ace
Squaresoft- FF, KH team, Xenogears, chrono series and Brave fencer musashi.
EDIT: Quantic Dream. I feel stupid to forgot about this.