Which oil paint brand is best when thin layer realistic painting & very subtle blends & high detail is desired

Answer 1

Depends on where in the world you are. There are many oil paints that can do this 'best'.

Old Holland
Holbein
Winsor & Newton
Grumbacher
Utrecht
Talens (Rembrandt)

Just be sure to buy 'artist quality' and you will have a great paint that will do it all. I'm not really a brand freak so I try a different color and brand every time. They all seem to mix pertty well though effects may differ somewhat.

Answer 2

If you are using them in glazing, not only the quality of the paints that you should consider, but you should also consider the opacity of the paints.
As for blending, even the highest graded paints are formulated differently from brand to brand, therefore they behave differently from one to an other. The best way to achieve the result you wanted is to "play around" with them, or make a color swatch book with all the paints you have.
As for the high detail, a desire viscosity can be achieved by using medium to thick or thin your paints.
Painting dosent have to always cost you a arm or a leg. Haha.