Let's look at your best options.
There are three buttons across the top of the UI that will get you to the various parts of the app. On the left is the unified Buddy List. This will show you all your contacts organized by network and any special labels you have added. Next over is the conversations tab. This will list your active chats and indicate which ones have new messages. You can long-press on one of them to close and remove it from the list. It will also indicate which service the chat is happening over. The last tab shows your active networks. You can disconnect and set statuses individually.
The chat interface is very slick looking. As you type a gray box will pop up with your text in it. This is handy because there's no text box taking up space when not typing. The only issue we see is that on most phones, you can't copy and paste in this non-standard text box. At the top is a pull down menu with all the functions you need to share content over chats. You can send GPS coordinates, pictures, or audio right from this interface.
We also like that Beejive uses the Android push API to send messages when you are not in the app. This means it won't have to poll a sever to get new messages, they will be pushed to the phone as needed. We've found the push to be about as fast as Google's Talk client. Battery use has been in the low to mid single digits for us even with heavy use. If you don't mind the price, Beejive IM is a solid messaging app.
Tapping on a conversation will open the somewhat spartan chat UI. It's just a plain white page with the text. All the messages seem awkwardly positioned. You have to rely on the labels to actually determine who said what as you go back over things. You don't get the nifty content sharing options like Beejive offers, but we will say this app is very fast. That's probably a consequence of the stripped down UI.
Meebo runs in the background to collect IM notifications. This isn't a snazzy as using the push API, but it gets the job done, and the battery draw is only a little more than Beejive. Notifications actually do show up very fast, sometimes faster than apps that use push. We do miss individual account status control. In Meebo you just have one universal status for your accounts.
Yes, Meebo is a less feature-rich app with a simple UI. But it is free and we have found it to be very reliable. Check this one out before you dive in with a pricey paid solution.
When you sign into Trillian, you go right to the contacts screen organized by service. The very top of this screen shows your Astra account info along with some handy icons that indicate which services you are connected to. If you have ongoing chats, they are listed in a break-out list at the top. Tapping on one will open it, but this isn't just any chat interface. You get a persistent bar at the top with all your conversations tabbed for easy access. This is one of the best systems for managing chats on a mobile device. The tabs are scrollable and indicate when your buddy is typing or has sent a message.
Trillian has the option under the menu to send a photo, but is lacking some of the more elaborate options in Beejive. Again, we don’t like that you can't control the status of individual accounts, but we understand why Trillian does this. Everything is handled through your Astra login. This is what allows some of Trillians more interesting features. For instance, Trillian uses the push messaging API to send notifications, and we found their servers to be reliable. You also get the handy ability to have IMs forwarded to your email automatically when you lose signal or log out unexpectedly. This is much like what the Android Talk app does.
Leveraging the Astra account setup, Trillian also has some great syncing options for those that use Trillian in multiple places. If you have ever left yourself logged in two places, only to find a dozen messages arrived in the client you weren't sitting at, this is a feature you will want. Trillian will now share your chats in real time between Trillian clients. Everything will be replicated in, for instance, the desktop and mobile app so you can go back and forth without missing anything. Trillian will cost you $5 in the Market, just half what Beejive costs.
Why you want a third party appYou could stick with Google Talk, but there is value in getting one of these IM clients from the Market. The first, and most obvious advantage, is that these apps will support more IM services. You can connect to more people and you only need to use one app to do it. It helps that these apps all support Google Talk as well, so you can completely turn off the integrated Google app if you like one of the third party options.
Apps like Beejive and Trillian also bring some unique UI elements to the table. While some of this is just eye candy, features like the tabbed conversation bar or individual accounts status settings are genuinely useful. These three apps aren't the only IM apps on Android, but we feel they offer a good cross-section of what is available. All of them are worth using. Do you run an IM app on Android? If so, let us know which one.