There's no one "best place" for a nav menu. The top, either above or below a banner, or on the left, are the conventional places, and conventional places are good because people are accustomed to them.
Very important are the design features of the nav menu: typeface, font size, color, borders, etc., all should work together to say "this list contains the main parts of this site (or app)". If you do this correctly, it should be obvious and clear whether menu is located across the top, vertically aligned on the left side, or even on the right side (but I would stick to the more conventional left side or top).
Another factor is the number of items on the menu: 5 or so items might layout nicely on the top, but more than that might require more than one line, making a vertical array on the left more attractive and clearer. The wording of the menu items and the font size factor in as well. As a very general rule, if I can comfortably fit it on a single line I put the nav menu at the top, otherwise as a list on the left side.
Most importantly: do not hide the nav menu behind a hamburger button unless you absolutely have to because of space constraints. There's plenty of evidence that unnecessarily hiding the nav menu is a UX mistake.