Stelios has a balcony view of the caldera, while Musses' balcony overlooks the sea across the "backside" of Oia. This is the main difference. It's still a very lovely view even though it's not of the caldera.

Musses has a more equipped kitchen while Stelios only has fridge and coffee maker. You can actually prepare food at Musses, although the equipment is minimal.

Both have sleeping lofts, TV and A/C. The decor of both is of similar quality.

Stelios is located right on the main pedestrian walkway so there will be foot traffic and I suppose a bit of occasional noise right below your balcony.

They are both situated in the same area of Oia, not more than 50 meters from each other. My favorite little bakery for warm breads, apple turnovers and spiral spinach pies is close by.

I've stayed at Musses twice and would not hesitate to do so again.

If you want to see a photo of the sea view from Musses let me have your email address.