This should be a list of apps I use for specific tasks and why I use them:
The free version allows access to all accounts you can reach with one ID. For me, this includes both of my accounts. What do you want more?
Read all descriptions for apps of this kind and decided that this one is the most powerful. Notifies you of upcoming birthdays, anniversaries or any other events from your Contacts and you can also add your own events. You can also load holidays for your country and get notified when you can stay in bed.
I'm currently evaluating both. Beejive looks nicer, but IM+ has Skype support. As I am no avid messenger, I can't tell about stability for now.
Looks like the best for Jabber/XMPP but is extremely instable if there are any connection errors. But it looks nice and supports all kinds of XMPP-Transports.
Since Shoutcast is THE online directory for radio streams, there was no comparison against other apps for this. iMediaSuite was already a "no go" after reading the reviews. I tried it and it crashed trying to read the contents of my UPnP server. PlugPlayer however worked fine and even shows album art.
I wanted a tasks app which syncs with some online database. I was happily using RTM for some time together with Gnome Do and directly per web. When looking around for some iPhone app I realized, that both iPhone apps need a $25/yr Pro account for the synchronization to work. As I don't use this so extensively to justify this yearly costs, I looked for alternatives.
Toodledo almost works the same, even a touch better I think. And for the iPhone app you just pay once - without needing a subscription at their site.
Twitterrific has a nice feature-set but is too far away from the iPhone Look&Feel. Tweetie was hyped everywhere as THE Twitter client for the iPhone, but compared to the recent version of Twittelator, it has to catch up now. The latter one got my money because of the vast features which are all easily accessible. The automatic preview of tweeted pictures is just icing on the cake.
The goal was to get a voice dial feature which doesn't send my voice or contact's names to some server for processing. From the reviews I learned that this is a slow process and it takes several seconds until the voice is analyzed and the results are downloaded back to the iPhone. Another goal was to have some automatic recognition which doesn't need to be trained. Using these criteria there was only one app left: Fonix iSpeak. Now if they'd only add more features like Voice Command for Windows Mobile has.