Should I buy Xayah or Zoe. I love both champs and I always either play mid or adc lane.
SOOO LIKE
or 
SOOO LIKE
or 
Zoe is an easier champ to main/use imo
is zoe a fun to champ to use over and over again?
if you're planning to main zoe, yes it's a fun champ.
Zoe if you're playing blind pick. If you're playing with bans, Xayah. Zoe has a very high ban rate.
I recommend Xayah, Zoe is likely to get nerfed soon and there is a chance that she will become useless like a lot of other new champions. ...but I might be biased because I'm absolutely in love with Xayah :D