Slide

It is open-source, ad-free, and subscription free.

• No subscription, and support for bringing your own client id
• Shows as many preview images as possible, and displays them large by default
• Supports Giphy emotes, Reddit emotes, and inlined preview images in comments
• It uses Material design, and the app is being updated to be more so
• Multiple accounts supported
• Supports multireddits
• Supports search of the frontpage, all, a subreddit, or a multireddit
• Supports subreddit, domain, selftext, title, profile, and flair filtering by keyword
• Extensive customization options including theming, font style and size, layout styles, thumbnails vs preview images, etc
• Backup and restore of settings

There is an active community for Slide on the /r/slidereddit subreddit, which anybody is welcome to join.