When you are hesitating on multiple IDEA

I choose the one I would enjoy working on the most.

Make a spreadsheet and model out what revenues could look like a 10, 100, 1000 users.

Then trust your gut.

Pick the impossible one..

The one no one will see coming...

Pick the one that they say ....cant be done

Decisions are made easier with more information. I would gather feedback about both ideas and the choice may become obvious.

Drop a coin, if your more excited that one side turned up over the other - choose the one you're more excited about.

Or If more than two:
Let a friend or your partner just Pick one. It will keep your motivation afloat If your own drive is declining