Some people say Zenith because it has a on/off asa and a zero system which Ive heard is basically nothing really. Zero system and on/off asa is the only difference between blitz really.
I have the Blitz and I love the gun for being my first electronic, its easy to take apart/tun and azodin has youtube videos of break downs. The asa on/off cost $25 on ansgear. There is no recoil on this gun
Koas is just a semi no electronic soo ya. But I choose Blitz because I can just buy a on/off asa and My gun doesnt leak so I don't need to turn the air off at all and Compressed air should only be used with these guns
I own a Blitz and I loved it when it was working. (I just need to take some time with it.) I think they are one of the best value markers Azodin has to offer. I don't think $70 is worth the few added features that the Zenith has.
On the other hand, the Zenith X2 looks very promising. 2 piece barrel (which the Zenith has now), CLAMPING feedneck, On/Off ASA, they already fixed the regulator issue, and hopefully the board will be user adjustable.