What is the difference between various modes in FPE? Format preserving encryption has three modes FE1( FFX) , FE2(VAES) , FE3(BPS) . All of them are based on Feistel Networks .Can somebody explain  how they differ from each other ?
Ff1,2,3 are basically inspired by LubyRack off constructions . At the core they differ in their round functions and key scheduling 

FF1 supports greater range of lengths and a tweak

FF2 generates subkey for each iteration to thwart any side channel attacks

FF3 has tweaks is split and used in rounding function, also the reverse the sub-strings of given input string while using in round function,

Both FF1,FF2 has 10 rounds FF3 has only 8 rounds 

Read more at NIST's 800 38 G draft