Fish tank input!

These are my 2 tanks right now. I'm still upgrading both of them a little at a time.

My fantasy theme tank

My peaceful/serenity themed tank:

I have decided I would like a third tank. They are 6.5 gallon tanks. I upgrade the filter system to a better filter in each, I also have heaters in each. They are nice tanks. Each tank contains 1 Betta fish, 1 albino Pleco sucker fish, and 1 fresh water snail.

These are the theme's I can't decide between. Which do you think my third tank's theme should be? Also, feel free to suggest a color of Betta I should get!

Drift wood theme:

Cutsie theme:

Ancient ruins theme:

Natural rock theme:

Planted tank:

A tank that contains live plants.