For a D3100, a kit zoom is usually the better way to start. A 50mm f/1.8 on APS-C is a short portrait lens, but it’s not very flexible for landscapes or general shooting, so using only that lens could feel limiting.

Between the two kits, the 18-55mm is the safer budget choice and is good enough to learn with. Kit lenses are decent starter lenses and can help you figure out what focal lengths you actually use before spending more.

The 18-105mm gives you much more range in one lens, which many people find more useful day to day, and some users prefer its handling/build. The tradeoff is higher cost, more size/weight, and more distortion.

The 55-300mm is not a replacement for a standard kit lens. It’s a telephoto zoom, so it won’t cover the wide-angle range that’s especially useful for landscapes.

So: if budget matters most, get the 18-55mm kit and add lenses later. If you want more versatility in a single lens, the 18-105mm kit is the better all-rounder. The 50mm f/1.8 is a nice future addition for portraits, but probably not the best only lens to begin with.