When comparing WhatsApp vs Relay for reddit, the Slant community recommends Relay for reddit for most people. In the question“What are the best Material Design apps?” Relay for reddit is ranked 4th while WhatsApp is ranked 34th. The most important reason people chose Relay for reddit is:
A great feature of Relay is the UX for swiping between the post and the reddit comments. It's very fast to go back and forth between the views.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Straightforward interface
The interface is very simple, fast and easy to use. You can start using it as soon as the app has been downloaded - it does not require setting anything up or registering. You can communicate with anyone in your contacts list that also uses WhatsApp. Includes useful features like seeing when a contact is currently available or typing.
Pro Widely used
WhatsApp reported 1.5 billion users in 2018. Your friends are most likely already using WhatsApp, so it's easy to get setup.
Pro Effortlessly builds your contacts by using your phone number as identification
WhatsApp will automatically find all of your contacts currently using Whatsapp and add them to your contacts. This makes it really easy to setup and given that it's the most popular messaging app it's likely that a lot of your contacts are already using it.
Pro Message mirroring on web app
WhatsApp can be used from the desktop via Chrome, Firefox and Opera browsers. Accessing it requires using the Android app to scan the QR code that's presented on web.whatsapp.com.
Pro Signal protocol
Whatsapp uses the state-of-the-art Signal protocol that ensure strong end-to-end encryption.
Pro One-on-one texts can be encrypted
WhatsApp has implemented end to end encryption for messages sent on it's service. Even WhatsApp has no way to read a users messages.
Pro Easy to flip between content & comments
A great feature of Relay is the UX for swiping between the post and the reddit comments. It's very fast to go back and forth between the views.
Pro Excellent material design UI
Relay uses screen space efficiently and can be navigated quickly. It is mostly designed for viewing a single subreddit at a time and making that experience as pleasurable as possible, with easy access to a subs from a dropdown menu at the top.
Pro Tons of features and functionality
With support for multiple accounts, interface themes, and inline picture previews, Relay for reddit offers a large amount of features for any power reddit user.
There are also many unique functionalities that set Relay apart from the competition.
●It has a 'Remove unread' option to swipe away all read threads. This is especially useful when it's a large and busy subreddit with tons and tons of submissions, to the point where it can get overwhelming. This a convenient option for making your reddit-browsing experience a little easier.
●It offers compatability with the Multi-Window feature which is present on Samsung & L.G phones (soon to be present AndroidOS-wide). This greatly enhances multi-tasking.
●It offers an excellent Spoiler tag support and an AMA mode (conspicuously missing from its biggest competitor).
Pro Allows you to view a parent comment
To keep a better context of the conversation, Relay doesn't hide the parent comment while browsing.
Pro Animations make for more pleasurable usage
The abundant animations make browsing more enjoyable because it transitions so nicely.
Pro Fast GIF loading
GIFs are automatically converted to gfycat format; they therefore load much faster than on other apps.
Pro Clutter-free and well thought-out UI
The moment the user opens Relay for reddit and begins exploring all of its ins and outs, it becomes quite clear how wonderfully designed this app is. There is excellent UX for redditors who prefer discussions and news, rather than pictures, videos, and gifs.
● You can alternate between a cards and a lists UI with a compact list view optional.
● A drop-down menu of all your subreddits is present at the top for quick and easy access. If the user is adequately familiarized with the list, he/she can simply swipe on the banner so to quickly switch between subreddits.
●The comment format option is situated right next to the drop-down menu.
It's an all around wonderful application with many Material Design elements employed.
Pro Automatically loads optimized images based on screen size
The app will automatically load a lower resolution image that is a closer match to your screen size to save bandwidth, with a button to load the original image if you need more detail.
Pro Easily save battery with night time theme
The available night time theme allows the background to be dark with light colored text, which uses less battery on AMOLED screens.
Pro Easily moderate from the app
Moderators on Reddit are allowed more functions over a normal user on Reddit, which is possible to be used in Pro for Relay. With these features included in the app it's possible to approve comments, check modque, and get specifically labelled moderator messages.
Pro Colour coded collapsible comments
Pro Smooth as butter
Opening links, animations, and transitions, as well as scrolling, all work well with no glitches or missed frames. The app feels extremely smooth thanks to the attention to detail in all of its inner workings.
Cons
Con Shares meta data with Facebook
WhatsApp shares your messaging meta data with Facebook if you do not opt-out in the settings. If you use the same phone number for WhatsApp and Facebook, the profiles can easily be linked.
See https://www.whatsapp.com/faq/en/general/26000016
Con Tied to carrier phone number
WhatsApp cannot be used by people without a smart phone with an active cell plan. If your phone is lost or damaged, or if your phone number changes, you cannot get messages sent by friends without them updating your phone number. You cannot send message to them until you are able to get SMS messages at your phone number.

Con Proprietary
Not open source.
Con Hard to migrate history cross platform
Migrating your chat history from Android to iOS or the other way around is not so simple. In some cases it requires a 3rd party app and in some the only way is to migrate specific chats one by one.
Con Web interface uses message mirroring
To use your computer to send messages your phone must be on with a consistent data connection.
Con Single device
You cannot use the same WhatsApp account on multiple devices (e.g. a tablet, a PC and a cellphone). The account is tied to the device with the specific cellphone number. Chat history is deleted when you sign in to a new account, unless you have created a backup.
Con No cloud sync
Messages are not stored on WhatsApp server for privacy and security reasons.
Con Limitation on shareable file sizes
WhatsApp now allows users to share files of any type, but there is still a 16 MB size limit.
Con Can not up/downvote comments
Con Can't disable sliding animations
Sliding animations are baked in & can't be disabled, as some don't like animations.
Con Non native image uploading
All images need to be loaded externally when wanting to view full screen, this means another app will need to be loaded, which can be slow and consumes RAM.
Con Poor feedback for network errors
Sometimes comment submission will fail silently and it isn't clear whether it went through.
Con Not open source
Accessing your reddit acount with proprietary software might not be safe.
Con No gallery swipe view
There is no way to swipe through a gallery of posts pics, which means each pic has to be individually clicked on and loaded, which takes time.
Con Sharing link/comment options buried too deep
At present, the sharing menu is buried deep inside: swipe an article > Click More > Swipe again > then Share.
