Matte or gloss, it's a matter of preference.
On the other hand, for your health and the environment, it's best to use an organic varnish (based on natural products), which you can find in organic stores or on the Internet.
At the very least, buy a varnish bearing the European eco-label, which guarantees, among other things, a very low VOC (volatile organic compound) content (compare with the major brands of varnish advertised in DIY stores: it speaks for itself!)
Beware: varnishes from specialist hobby brands can be just as harmful.
Don't use solvent-based varnishes (which can be washed off with white spirit, not water) such as Pébéo's old-fashioned varnish, which is attractive because of its amber color, but gives off very strong, unpleasant odors even long after the object has dried.
always varnish in a well-ventilated room, away from children and pregnant women, and wait several days before installing furniture or objects in the home.