Yellow phase eyelash vipers are pretty up there for me.
If you were to ask me about something I could actually keep though I'd have to go with BRBs, GTPs or the good old fashion ball python haha
Edit: After reading through some posts I realized I forgot to put Rhino/Gaboon vipers. Every time someone mentions those I think of Gabby and Mr. Sniffles from the old viper keeper videos haha