The Unlicensed Bands
A very good antenna to use for maximum range. Use a length of wire (or a PCB track) 1/4 wave length (e.g. 172mm for 433MHz). The optimum is to use the wire straight, but it can also be bent into a 'L 'or 'U' shape if necessary (it will reduce the range a bit but it still works well).
A wire antenna is better than PCB loop
Helical (Coil) / Spring antenna
Also commonly used.
Good for ease / low cost of manufacture, but range is reduced.