I've been using Printopia for a few months now. I have an old Brother laser printer, a Canon Inkjet, and a new Canon MF4350D. I tried both of the other apps but found neither allowed me to use the duplex feature on either printer. With the MF4350, the other two apps only printed the first page and then stopped working! At work, some of our printers have passwords, and again only Printopia allowed me to print to those. It seems Printopia is a complete implementation of the AirPrint protocol, as all of the features work properly, while the other apps just seem to trick the iPhone into thinking it's talking to an AirPrint device when it's not- which explains the problems and the prominent disclaimers on the other apps websites. Printopia is well done, you can tell they've put a lot of work into this.

Incredibly well done app. I've been wanting to write my own to-do list application for a long time, and now I don't have to. I just switched from OmniFocus, which was decent, but hasn't changed much in a few years and didn't handle synchronization well at all. As a developer, I appreciate the considerable recurring costs of maintaining servers, and the need to charge for sync. You only pay for the app once- but you could use the sync service for years. Developers get billed monthly for servers, bandwidth usage, and also have to pay people to maintain, backup, and manage the servers- so you continue to have a seamless sync experience. At $20/year for sync, this is a steal!