How can I make this smooth without Ngons or pinching?

Giuliano_Patricelli

I can't find a proper edge flow to make this all smooth without Ngons. I want to keep a slightly hardened edge without the pinching seen in the top half of the image 

Nominous

Since it involves curvature, the correct way is to make your cylinder's sides about 14 times as dense (based on the current width of your support loops for that detail) so you can run those two support loops down vertically and avoid pinching. Alternatively, you could use something similar to Blender's shrinkwrap modifier or 3ds Max's conform compound object in order to snap the sides of this object to a separate cylinder that has smooth sides. If you wanna stick with what you have, I found that something like this results in the least pinching, although it really messes up if you add an edge loop below this area:

FrankPolygon

Use the existing geometry on the cylinder walls as support loops. Block out the subtractive shape and adjust the segment count of the cylinder until there's sufficient supporting geometry and the subtractive geometry lands between the edge segments on the cylinder walls. Add support loops and merge into geometry that runs perpendicular to the edges that make up the wall segments.

Depending on the object's size and the view distance the width of the support loops and the number of cylinder segments can be adjusted to tighten up the edges. That said: try to use the minimum amount of geometry required to accurately hold the shapes. The faces between the outer edges of the shapes and the inner support loops can be used to take up most of the positional difference between intersecting geometry elements. No need to over complicate things with superfluous geometry.

It's also worth mentioning that unless there's a hard technical requirement that precludes the use of n-gons it's fine to use them as long as they aren't generating subdivision smoothing artifacts. There's more than one way to approach modeling this shape and some of those methods would include using n-gons or triangles where appropriate.