V3 is my favourite game because it spends the most time on the friendship between Saihara, Kaito and Maki (whereas other games relegate those things to free time events, meaning they're never really integrated into the plot) and because its finale is by far the most brutal one. Aside from barely anyone surviving, the survivors basically suffer complete ego death and then decide the only way forward is to collectively commit suicide, that's omega based.
Also it has Tenko.