Whilst Apple has stuck to the classic 4:3 ratio (4032x3024 pixels), I have preferred 16:9 on my latest Android phones, Nexus 5 (3264x1836 pixels) and One Plus5 (4608x2592), especially for landscapes and for viewing on most phones, laptops & TVs. The1+5 also offers 4:3 (4608x3456) & square (3456x3456), which avoid the darkened section of the view when taking 16:9 photos.

Google Photos from OnePlus5 Photos | Add to Album to upload to ccpcgc album, where you can edit | crop/rotate | aspect ratio | 4:3 using Mac or Chromebook. Or you can edit on phone, save a copy and add to ccpcgc album, so original 16:9 photo stays on phone.

Preview on Mac

I am also experimenting with cropping existing 16:9 photos to 4:3 in Picasa (Windows10), defaulting to 3456x2592 pixels. I'm trying to avoid further cropping, to avoid pixellation.

Chromebook Image Editor closest default crop ratio is 6x4 (say 4x2.67). A freehand crop to 3537x2592 is slightly closer to 4x3.

Snapseed on Android OnePlus5 has a default crop to 4x3, which you can export to a selected folder. It has slightly annoying default renaming , but filenames can be changed in that folder.

I upload these to Google Photos (cjcpc@outlook.com) from my PC (not from within Picasa, which no longer works), and name and share the album. Remember to upload photos not albums if you crop or modify any photos, to avoid uploading the originals as well.