Based on your questions, you are not a collector, but an interested shooter, so forget about the small stuff, like octagonal vs round, or high wall vs low wall, etc... Buy PURELY on condition. There are refurbed 91/30s on the market that are like new, and many M48s are unissued. DO NOT TOLERATE A WORN OR PITTED BORE!
The 91/30 has better sights, but the Mosin action is a bit clunky, and this is made worse by a low leverage handle. Note that the Mosin Nagant action was designed in such a fashion to avoid infringing on any patent issues. The M48 has a much smoother action, but it has the horrible mauser barleycorn (triangle) front sight. The Yugo will show better finishing craftsmanship.
It will really be a personal decision because they are both effective pieces. I suspect you'll end up with an M48 because it's more of what US shooters are used to. My only real advice is to make sure the bolt head and bore ARE NOT CORRODED. If they are, the pits will give fouling a nice place to hide, and this is not what you want with corrosive ammo.