Here are my ideas for tilesets that I want to make:

Mine of the lost Canyons Day/Night - Rocky desert that has a mine with crystals, lava, mine carts, ect.
Aquatica - Underwater tileset with a base and lots of eyecandy.
Clock Factory - Mechanical stuff, conveyor belts, anything in a clock.

The problem is that I can't decide which one to make (or start it for that matter). I would really appreciate some advice.