Buy the top grades of either.
Use good roller-covers and good technique.
Clean (POWDERED Dirtex is my fave, and I recommend it to our customers frequently) and possibly prime your walls.

Yep..."sheen" is relative, kinda like shoe or jean sizes!!

My FPE Eurolux Matte is shinier than our C2 Eggshell!
(EXTREMELY good paint though!)

Faron

"Best" grade in SW is usually assumed to be Duration. Duration eggshell has a generous edge of gloss to it. If we pretend that there is a scale for eggshell sheen, Duration eggshell would be plotted on the higher end toward glossiest.

Pittsburgh Paints Manor Hall or Manor Hall Timeless are both excellent options out of PPG - gorgeous final finish for both. On the imaginary scale for eggshell, the Manor Halls would be at the opposite end from Duration. They are far less glossy - more like a "matte eggshell" than a glossy one.

Both brand's best grades are excellent options at fair price points.

I've recently used SW's Duration Matte. It looks flat when you look at it straight, but there is a slight sheen when viewed at an angle. Beautiful paint, with good coverage and no splatter.