Because I have been asked (and it seems a useful reference to make), here's a roughly tiered list of characters from media who most often appeal to me in terms of making TFs. The list is non-exclusive (your favourite may qualify, I just don't really know them) and in large part based on appearances / design / general vibes (since I don't do mental character TF and probably haven't seen any/all of their respective franchises). With one exception I have steered clear of including OCs, and sonas are off limits (although one or two would make it up here).

This list is roughly ordered by tier, but all of these would (for me) rank A or above on a regular tier list.

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Falco (from Starfox)
Tigress (from Kung Fu Panda)
Bowser

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Robin Hood
Kovu (from The Lion King 2)
Nick (from Zootopia)
Robbie Sinclair (from the sitcom Dinosaurs)

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Scar (from The Lion King)
Judy (from Zootopia)
Alex the Lion (from Madagascar)
Donald Duck
Ember (AxiomTF character)

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Fox McCloud (from Starfox)
Maid Marian (from Robin Hood)
Ratchet (from Ratchet and Clank)
Diego (from Ice Age)
Anubis "Doggie" Kruger (from Power Ranger S.P.D.)
Timon (from TLK)

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Don Karnage (from Talespin)
Minnie Mouse
Mobians (from the Sonic franchise)
Foxy Bingo (from UK TV ads)
Na'vi (from Avatar)
Brooklyn (from Gargoyles)
TMNT

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18 Drawn (at least one public sketch), 7 Not Drawn (Yet).
19 Male, 6 Female.
3 feral (of which 2 are TLK)