The style on the left is going to be less infuriating when it comes to animations and drawing other characters. Take it from me that keeping it simple is definitely better. My own game went through 3 distinct art styles before I finally landed on the one I wanted. You might find yours will grow organically too as you develop the game, so if you keep it simpler now you're setting yourself up better for future changes.
As for having two different sprites, that's up to you. I'd use one for now and if you feel you want to have a distinct sprite for isometric and platformer then add it in later.