Unless you are in a big hurry, wait about three months. There will be a much wider selection of Android tablets, some with Gingerbread on them. Maybe even a few with Honeycomb. Also the second generation iPad should be announced.
The OS upgrades for Android should make a huge difference in the usefulness of those tablets. iPad's will be upgrading the hardware, I hope, which will have a big impact on their abilities.
Now, I have an iPad, and I love the thing. That makes the rest of what I have to say a bit biased, even though I'll attempt to be even handed.
Both the current iPad and the Android tablets have been called just bigger versions of their respective smart phones. There is some justification for this, more so with the current Android tablets than the iPad. The people who say this though have their own use case for the devices. The final judgement should always be based on what you will do with the device.
They are both good at video, pictures, books, and web access. Flash may or may not be a deal breaker for you. Keep it in mind. Personally I rarely find a page I can't browse on my iPad, but that's my use pattern.
The iPad is the leader in games and most other apps. Not because of capability of the hardware, but because there are simply tones of great apps available. While some argue that you only need one great app for each use, the truth is that if there are three great apps then the developers are under constant pressure to improve them. This will even out in time. Probably no more than another year at most.
Android is vastly more customizable. On the other hand the old saying, "What you can do, you have to do." applies. The stock settings are rarely better than ok, and if the OS follows suit with my Droid X experience you are going to end up doing some minimal digging around, just to get it to work the way you think it should.
The iPad is much less customizable. The interface is pretty much set in stone, with only minor cosmetic touches available. On the other hand I have yet to have an iOS device suddenly stop working properly for no apparent reason. I can't say the same for my Droid X, though so far the issues have only been minor annoyances. You can argue the wheres and why-fors all day, but iOS is more stable. Again, Android should be catching up with this with each update.
I should also say that my stability comments are based on a phone vs a tablet. Phones often have more stuff going on in the background, so the difference may disappear when comparing tablet to tablet.
My final argument is for the iPad. Not because I think the Galaxy Tab is a bad choice, but because I think having one of each device is a big bonus. I mean seriously, I never have to be gloomy because the other platform has some great app that I can't use.
I'd buy one of the new Android tablets too, if my budget permitted.