Sorry, I know little about both rifles but at first glance my though would be the lever action (Winchester, right?), only because it has a faster follow up. Then I see the .303 British, one of my favourite rounds. I have a soft spot for the .303 Brit and under the right hunting conditions all you need is one shot. The lever action would make more sense but I would personally go with the single shot. I am guessing it is a Ruger No.1? Only advantage of the single shot over the lever is that the .303 is a more capable round, IMO.