if you mean plastic 'from scratch' kits, tamiya and fujimi tend to be the best for the money, revell and airfix etc being cheaper and less detailed.

if you mean 1/18 diecast (which most of us have) autoart, kyosho, sunstar, minichamps etc are all decent brands- but even cheaper brands like bburago and maisto can be made into something nice if you have the time and skills