They do have a different wave length and that says a lot...
The 433MHz one should behave better on narrow environments, so if your application stays inside then it's better to have that module... On the other hand 315MHz have a longer wavelength and you will get a little bit more range outdoors in an open environment...
Keep in mind that this modules may not have encryption which is vital...
Manchester encryption is an option and quit easy to utilize...
Also the antenna should be different in case you make it and don't buy a pre-made...
λ/4 straight antenna is a good one.... where λ is the wavelength...
λ/2 straight antenna is an option too... but it gets rather long...
To calculate the antenna length the formula is
c = λ*f
Where: c is the speed of light in vacuum space and proximately in the air medium
λ is the wavelength
f is the frequency of the wave hence the frequency of your transmitter
That's it for now... If you want something else... FIRST Google it, then ask ;-)