I have both an iPad and a Lenovo Thinkpad Tablet 2 (Windows). The thinkpad is smaller and has a more travel-friendly shape in my opinion. In addition, it runs full Windows which means I have all my desktop applications available.

For productivity/work purposes, the thinkpad is better. If I was going on a tour where I wanted to get my work done remotely, I'd pick the thinkpad.
For general web browsing, playing videos, etc...basically entertainment purposes, the iPad is better. If I was touring and just wanted something to watch Netflix or browse the web, I'd pick the iPad (or an android tablet, probably the Nexus 7).