If you think being first-to-market is important in your niche and your time-to-market will coincide with some competitive tablet launches, then go for Android.
I contest that! Do you know the market? Have you tried a few competitors? Maybe you have, and maybe you don't like them, but they're there!
Far away in the Asian region, I am pretty sure they are already concocting a tablet running Android that would only cost less than $100.
Take the Archos 101 WiFi tablet: 10.1" screen, amazingly light with 480g (the 9.7" WiFi iPad weights 40% more, even the 9.7" Kindle is over 10% heavier), very good battery life, USB client & host ports, actively supported and updated (since the update to Froyo all earlier software glitches are finally gone), optional Android/Angstrom dual-boot feature for embedded Linux hackers, and all that at a really low price.
And guess, does anybody care? Zilch! There are just to freaking many Android tablets, and there is just one Apple iPad (okay, two: WiFi and 3G). I despair...
Edit: To clarify, the iPad alone gets about as much media coverage as all the Android tablets combined, and that's the crux right there!
I would suggest webOS. The field is less crowded, you will stand out, and make iPad and Android people say, "Why don't you do that for us too?"