(Yes, I collected the images and made this comparison on my own)

My favourites are Gen1’s (and Tales, I put it there as it was a seperate show)
Gen3’s is pretty nice
Gen3.5 makes me think of Littlest Pet Shop (they are cute, and I love them but MLP is seperate...), my least favourite
Gen5’s and Gen4’s aren’t really that great... they are alright but not my favourite
I do like G5’s a bit better than G4

Best to worst: G1, G3, G5, G4, G3.5

What’s your favourite muzzle/head shape?

G1 and Tales

You should also include G2

i go for G1 more Equine face muzzle

Kind of hard for me to pick, since I like all of them.

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Tales.

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Hmmm... I guess but it didn’t really have a show

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It did have a PC game

Tales