I was testing a new topology optimization software, and having issues with a real life part, decided to try the simplest thing I could think of: A shelf mount. This part is optimized for maximum load with minimal material use. The screenshot shows the part under a 50 kg (110 lbs) load (!), with material stress staying under 20 MPa.
In addition, the part is designed to print completely without supports. Print time around 5 hours on my Prusa i3 MK3s.

Print instructions

Category: Organization Print Settings

Printer Brand: Prusa

Printer: I3 MK3S

Rafts: No

Supports: No

Resolution: 0.2mm

Infill: 100%

Filament: Doesn't matter ABS or PETG
Notes:

It will probably also be fine with 30% infill, however in that case the permanent compression under the screw head might cause long term problems. 100% infill doesn't add a lot of material, since most of the part is already very thin. Print with at least 2 shells, 3 is better.

How I Designed This

CAD work with SolidWorks 2017, topology optimization with ANSYS Discovery Live Beta.