When comparing IMO vs TeamSpeak 3, the Slant community recommends IMO for most people. In the question“What is the best team chat software?” IMO is ranked 20th while TeamSpeak 3 is ranked 22nd.
Ranked in these QuestionsQuestion Ranking
Pro Video call support
Pro Beautiful User Interface
Although IMO has a comparable, and in some cases superior, feature set when compared to the competition its key selling point is its interface.
From LifeHacker when it won "Best IM Client":
Signing on, navigating chats by tapping the tabs at the bottom, searching for buddies, and virtually any other operation is easy to find and use. The app, itself, is very quick. Even sending a voice IM, if you don't feel like typing, is responsive and sends quickly. Everything imo does it does well, but it's excellent navigation really makes it top notch.
IMO also has a fully functional website that you can use for chat while on your desktop or laptop. This really puts IMO ahead of the competition as you can use the same system on all your devices so you don't have to deal with overlapping notifications etc. (Note: IM+ also has this feature)
It should also be noted that it has the highest rating in the App Store due to both the UI and its stability.
Pro Easy to switch between conversations with tabs
Tabbed chats make it easy to switch between conversations
Pro Lists and chat histories are searchable
Both your buddy lists and chat histories are searchable.
Pro Accounts can be linked so you don't have to sign in to several accounts
Pro Push notifications
Pro Concurrent sessions
Concurrent sessions allow you to be logged in on your desktop while also being logged in on your phone.
Pro Chat groups
Pro Fine-grained administration options
Allows for complex administrative structures, with lots of roles and many other features related to server administration.
Pro Works on all main PC OS platforms
Available on Windows, Linux and OS X allows for a user to choose what best OS suits them and not have to worry if their game chat software will work.
Pro Supports audio and text chat
TeamSpeak allows for both voice and text chat. this adds flexibility, and can clarify information if somebody has a very poor connection, or a very thick accent. It also allows players without a mic to communicate with the other players.
Pro Widely used
Among most MMOs (massive multiplayer online games such as Guild Wars 2, or World of Warcraft) Teamspeak is widely used so it's likely other players already use it and won't need to download a new program. There are also many knowledge and help articles available online.
Pro Voice Activation Detection while using Push-To-Talk
Pro Echo reduction
Pro Free for non-commercial use
As long as one is not using TeamSpeak for commercial services the app is free to use. This is great as most users will not be using it for commercial purposes (as long as you aren't making money off it you don't need to pay for it) such as gaming.
Pro Sound level tuning
You can tune everyone's sound output levels to meet your own personal preference in inbound volume. So to your ears nobody is too loud or too quiet.
Pro A lot of features
Pro Unlimited nesting of channels
This allows for very granular organization.
Pro Supports Encryption
Under "Edit Channel" --> "Advanced" --> theres a toggle button called "Voice Data Encrypted". Everything but file transfers is encrypted.
Pro Private hosting
You can host your own server.
Pro Plugin support
A wide range of plugins are available for those that want extra functionality, ranging from soundboards and overlays, to peripheral and application hooks.
Pro TeamSpeak Sync
Signing up for a MyTeamSpeak account will allow you to synchronize your bookmarks, identities, hotkeys, whisper lists and channel subscriptions across all devices. MyTeamSpeak features will include addons synchronization, addons update management, and more.
Pro Clean theme
Pro Advanced permissions
It has an advanced system to manage channel/server permissions.
Pro No privacy nightmare
Con No support for third-party instant messaging networks
On March 3, 2014, IMO will start discontinuing support for all third-party instant messaging networks.
Con Mobile app costs money
TeamSpeak for mobile platforms costs $1.99 for Android devices in Google play store or $4.99 for devices that run iOS.
Con Requires to self-host, rent or use a public server
TeamSpeak cannot be used without a private server (meaning TeamSpeak themselves do not provide servers). This adds complexity to the setup and may simply be out of reach for many users. There are, however, several free public servers available, Teamspeak offers to rent one, and many games have dedicated servers available through their respective websites.
Con Outdated UI
The client itself feels really old, and even though there are custom huds, most of them don't feel modern.
Con Too easy to hack
Hacks can be used to gain admin controls of a server, locking players and admins out.
Meanwhile, your server is renamed, passwords changed, hacker leaves it open to the public but all the members are banned along with the admin of the server. The only way to deal with it is to close the server, delete it, and open a new one.
Con No video communication
Currently there is no video chat for the app. While not essential for in-game communication, outside of the game it would help to strengthen online relationships with your gaming pals.
Con Proprietary software
It's not free.