[Sin]

MyBB is free for a reason...
IPB > All, no questions asked.

IPB has more hooks/add-ons, better looking skins, better developers, a MUCH bigger and better community, more customizable skins (along with it being easier).
The ACP and MCP are easier to use, and have more functions and tools for you to use, making things easier on everyone.

I could go on and on, but I'm too lazy to right now.

So, you are an IPB fan ?