Many people use a variety of differing paints and techniques. Generally speaking, the military models with color are given a flat finish to look more realistic, or true to scale. The exception to this is military models (DC-3, B-29, P-38) with a bare aluminum or metal finish. Since bare metal has a glossy looking finish, a semi-gloss or gloss paint would achieve a more realistic look. Most civilian aircraft like the Cessna or Beaver can also use a high gloss paint to look more realistic.
Some people use airbrushes with really nice looking results. Others use a brush, some use spraycans. Some use no paint at all. Just plain or colored tissue. All techniques have yielded some awsome looking results. I would suggest going through
lots of older posts on this forum at specific aircraft, see what results you like, and try those techniques.
One thing that some people do to get a higher gloss or deeper looking finish is use a clear gloss-kote spray like
Testors after the painting and decals are done. Some also use
Future brand floor polish.