Using IRC chat is a big deal for Mac and iPhone developers. It's a great way to find peer-to-peer support. Sites like Freenode and OSX86.hu give you access to hundreds of other developers to consult with in real time. Engineers from a major fruit-named corporation frequent popular chat rooms, offering unparalleled technical access. Having a useful IRC client on the go can be golden, so it was important to me to find a good one for the iPad, and both of these clients are excellent.
When it comes to price, Colloquy is the clear winner. The iPad version of Colloquy sells for US $1.99 at the App Store. Linkinus costs about four times more at $7.99 for its iPad version. In terms of bang for your buck, both are good buys, though. I don't think you'll be dissatisfied with either one.