I've owned both in both Phone and Tablet sized devices. Both have their uses and audiences.
Apple iOS if you want something that works and is reliable, not to mention is a pretty nice tool for use in graphic arts (certain styluses can turn some models of the tablet into pressure-sensitive graphic tablets with the right application). Also great for first-time mobile users. And if you ever have a problem, Apple has some of the best Customer Service in the industry.
Android is great if you know what you're doing. These are more high maintenance machines, but each one by various manufacturers are unique. I fell in love with the Transformer Pad line of tablets by Asus both for their incredible specs and that they were one of the first tablet lines that had a dedicated docking keyboard that expanded the capabilities; including extended battery life and USB 2.0 Slots. Also the Gorilla Glass on these models is so mind-blowing I love freaking my friends out when I start trying to scratch it with a knife (never leaves a single scratch). I've also had good luck with Samsung, though admittedly beyond the pressure-sensitivity on the Galaxy Note series there isn't anything really pushing me to buy one.
The only thing that people need to know with both is KNOW HOW TO PROPERLY CLOSE APPS. Both use the idea of clearing your recently visited apps, but every android distribution will have a different way of doing that, some (like the early Motorola Droid models) don't even use that feature at all and require you to use a less than functional app-killer program (3rd party app-killers are only slightly more usable).