Either rifle will obviously suffice! However, Nilgai are extremely wary and spook easily. The lighter rifle might make for a more enjoyable hunt as one can spend a tremendous amount of time stalking those antelope.
My first hand experience with .366 250gr. AB is rather limited. I've heard from some extremely reliable folks that it penetrates and hold together well.
I've used the 250gr. TSX with excellent results. I like the 286gr. Nosler Partition. I personally haven't seen much of a velocity increase (less than 100fps) with the 250gr. bullets, so I've settled on using 286gr. NP for everything.
