Ultra from the advertising, other than that noone really knows as all they are going from is the advertising... People ask a lot about best oil to clean, but very little hard data, or pictures before/after of which oils they tried, and the pictures of before and after.. valve cover would be pretty easy.. I wouldn't pull a cover off either if it were still running.
Next up is MMO, or one of the other cleaning, aldoer chemicals/agents.. If the only had a scrubbing bubbles, man that would sell like Clearance Group IV/V oil at $2 a gallon...pick your boutique or favorite oil to dream about here LOL