Any conductor can be used as an antenna. If it will conduct electricity then it -can- be an antenna. Length of that wire also plays a part. That length is in relation to the wave length of the frequency being listened to. "Tuned" lengths, having a 'special' relationship to the wave length of the desired frequency is a nice thing to have. The 'bad' part of that is that the length changes with frequency, meaning that it may or may not be particularly conducive to hearing stuff on some other frequency. All that means is that reception may be less than 'optimum'. That isn't a 'killer' in it's self, I don't think I've ever had an 'optimum/perfect' antenna and haven't missed much. (This says nothing about impedance matching, or propagation! That impedance matching isn't that big of a deal to most receivers, propagation is!)
Different antenna 'styles'/shapes have different reception characteristics. Those characteristics can usually be changed/improved by simply moving the antenna, 'pointing' it in different directions, getting the thing higher, maybe changing your socks?
What all this amounts to is that no single antenna is the 'best' in the world. No matter what the advertisements say...