Adhesion is the paints ability to grab on the surface without peeling.
You have to remember one thing. No matter how good the adhesion is, if you are going over oil paint you always have to prime first.
As the paint dries, leveling is the paints ability to "level out" in a way that you don't see the brush strokes.
Some semi gloss trim paints have amazing coverage.
However, with some of the inferior paints on the market, even the second coat may not look fully covered. This is why choosing really good trim paint is essential to getting a paint job that has an amazing finish.
So to answer the question what is the best trim paint?
My favorite trim paint is Benjamin Moore. Not just any of their products, specifically "Regal Select" semi gloss for the following reasons:
Being a long island painting contractor for over 40 years, as you can imagine, by this point I have used all the top brands out there.
Paint such as Sherwin Williams compare as far as staying white, and adhesion. (not the cheapest lines)
Regal Select differs in leveling, Here is where this paint excels above the pack. None of the other paints even come close. When painting trim, the brush strokes almost vanish.
Especially on new doors, or doors that are in good shape, the finish will look like a factory finish.
I don't want to overstate what the Regal Select can do for you. If you have molding installed within the last 20 years, or if your molding and doors are in mint condition then the Regal Select will look amazing.
However, if you have original molding from the 1950's or before that has many layers of built up paint, then no paint is going to make that look new. If you want it to look new, it probably will need to be replaced.