Differences between 2nd order low pass filters
One is Salena Kay, and the other I don’t know what is called.


Sallen Key with unity low pass gain: -



Pictures taken from this useful web calculator.



Sallen Key with gain setting resistors: -



Pictures taken from same calculator page as above - scroll down



MFB or multiple feedback: -



Note that the low frequency gain of the above MFB circuit is \$-\frac{R3}{R1}\$

Pictures taken from this useful web calculator.


  Question: what is the difference and which is better to use?


The MFB uses one more component but can operate at higher gains. I suggest you use this information (and knowledge of your application) to google for further information.