Best Wallpaper Sites as Recommended by Reddit Comments:

Wallpaper Engine

• Known for custom (animated) wallpapers.
• User quote: "I’m not sure if there are better options but I use Wallpaper Engine for custom (animated) wallpapers."

Rainmeter

• Ideal for custom desktop themes.
• User quote: "Rainmeter is also very cool for custom desktop themes."

Wallbase

• Recommended as a favorite wallpaper site with a good collection.
• User quote: "I think Wall paper is irelevant. Ur set up is tidy enough for constractive work ... cld mayb block the sun out ..."

Interfacelift

• User quote: "http://Interfacelift.com is another good site."

SimpleDesktops

• Praised as one of the favorites for wallpapers.
• User quote: "This site, and SimpleDesktops are my favorites."

Wall.AlphaCoders

• Mentioned by a user who uses it.

Wallpaper Flare

• Described as the best by a Reddit user.
• User quote: "https://www.wallpaperflare.com/ the best for me 👍"

Unsplash

• A platform with a lot of free wallpapers, promoting photographers and artists.
• User quote: "Unsplash.com has a lot of free wallpapers. Basically it is a platform for promotion of photographers and artists and they have a lot of free images."

4walled.org

• Recommended by a user as their preference.

Tapet

• A wallpaper app that is random, customizable, and regularly updated.
• User quote: "I personally like Tapet. It is random, customizable, and updated pretty regularly."

Muzei

• Suggested for rotating wallpapers from various subreddits like r/EarthPorn.
• User quote: "I use Muzei and Vitrina to rotate wallpapers from subreddits like r/EarthPorn and r/SkyPorn and even r/ImaginaryStarscapes"

Vitrina

• Used alongside Muzei for rotating wallpapers.

Reddit

• Mentioned for finding wallpapers from subreddits like r/wallpapers or r/verticalwallpapers.

Abstruct

• An app on Google Play Store with stunning wallpapers designed by the same artist who works on OnePlus wallpapers.
• User quote: "Look up Abstruct on google play store. the wallpapers are made by the same artist who designs the wallpapers for oneplus and they're stunning."

Bing

• Liked by a Reddit user for wallpapers.

Backdrops

• High-quality images available on this wallpaper app.
• User quote: "Backdrops is a pretty good wallpaper app... They don't have much branded stuff but have nice artwork and picture wallpapers."

Walli 4K

• Praised for offering great options, especially in 4K resolution.
• User quote: "Walli is pretty great, and it has a lot of options."

HDQ Wallpapers

• Recommended as "AMAZING for wallpapers".

NASA

• Recommended for space-related wallpapers such as images from Hubble or spacecraft concepts.
• User quote: "but I'm personally more on the spaceflight side so I'd go for google images, google whatever spacecraft concept I'm into at the time"

Mars 2020 Rover "Perseverance" Raw Images

• Official source for background images.
• User quote: "I use the mars 2020 rover " Perseverance" raw jpgs as my background."

Hubble Website

• A source for space-themed wallpapers.
• User quote: "I used to get all mine from the Hubble website."

This comprehensive summary outlines various wallpaper sites and apps recommended by Reddit users based on their preferences and experiences.