A question of variety

I'm curious what most people think is better. Having more different designs or having the same design in different variations.

Let's take the current shop-addition for an example.



Would it be more interesting to have the same skull in different colours (maybe a red or blue spirit coming out of it's mouth, different eyecolours, etc) or would it be better to have a completely different design in the same style (a big cat/horse/goat skull with a spirit coming out of it's mouth).

Personally I'm torn between both ways. I love to have different colour versions but I can't offer too much at once. There is also the option of rotating the designs.

For example:
First week = Skull with green spirit
Second week = Skull with blue spirit
and so on...

As said, I'm really having problems to choose here.
Feel free to post your opinion. I'd be really thankful for any kind of input.