Probably my AR-15.
It's the type of rifle I've used the most and know the best. The flat top and forearm rails give it a lot of flexibility with types of sighting system. And there isn't anything around here I can't hunt with it. Finally, with the right set of equipment it's fairly night friendly.
I like walking around with my Winchester 94 better. And it's prettier. But, if I could only have one, I guess I'd give it up.