choose Sergei A1 over Khadgrim good?

i have Sergei A0 thinking about choose him over Khadgrim and try to summon next week. is it good choice? i have Valderon A0, Dracula A3, Eirlys A0, Diaochan A3. want to push higher on Arena ST. will it good choice? also i have Gretchen A0