I would go with Dr Falkenstein over any of those 4* on the list because in mono he is -16 Opp Attack, min 8
Corvus has only 3 damage... 5 is almost double.
Frankly, only one you have any reason to change is Lorna, and even then only if she doesn't fit your playstyle. And even then you'd have to choose from Andy Ld, Cley, Danae, (Deebler), Snowflake (and Zeke).
Mono Skeelz? it is no brainer, pick Dr Falkenstein
don't worry, his price will go down in time (his price will go down every 2 weeks until it hits the point, I think around 2-3K?)
if you want more damage, I suggest to change Praxie or Lorna to Zeke