IMO vs Campfire

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.

Tabbed chats make it easy to switch between conversations

Both your buddy lists and chat histories are searchable.

Concurrent sessions allow you to be logged in on your desktop while also being logged in on your phone.

You can invite people to join conversations even if they don't have a Campfire account. Campfire will generate a link to share and the guest will only need to enter their name to join the conversation.

When you need to make a conference call, all you need to click is "Start A New Call" and Campfire instantly embeds a phone number and password code in the message thread.

Campfire supports only iOS, but third party apps can be used for Android. There are also other third party apps that build upon Campfire and extend its functionality.

Images that are uploaded in the GIF, PNG, or JPEG formats are represented as thumbnails in the chat room.