How popular is Izik? 

Izik is an unusual first name for men.  Izik is an unusual surname too for all people. ( 2000 U.S. Census)

Which version is better? 

with its source form and related boy names.  Prominent variation forms of Izik (unlisted) are Isaac(#31 a year ago), Issac(#562), Zack(#1217), Izaac(#1366), Isaak(#1412), Isa(#1496), Ike(#1676), Izaak(#1712), Zak, Isak, Isac and Izak.  Adoption of these forms of Izik was common in the year 2012 (adoption of 0.6%) and has remained as widespread to this day (adoption 0.6%, down 4%), but with the version Ike becoming somewhat dated.  Isaac has been the most well-known version. ( Top 2000 Names, 2015)