Today I got HC-12 modules, with two different wire antennas. Both are supposedly for 433 MHz but one is decidedly bigger than the other. The silvery one came with the module and is much smaller than expected; the golden one I ordered separately and is the size I expected.
I know next to nothing about antennas, I normally stick to the rule "bigger is better". Of course I'm looking for maximum range - in the final version of this project I think I'll be using external antennas (attached to the U.FL connector).