Honestly, there's really no reason you even need a physical tablet for just basic app testing. Just use the emulator that comes with the Android SDK. Then you can post a beta and let all the Android users here take care of finding any device-specific quirks. The emulator has the advantages of being free and you can change the android version, screen size, and pretty much everything else at will.
But if you do decide you want an actual tablet, I agree with the others who said that it really doesn't matter what brand; just pick one that matches the size, power, storage, and price that you want. And I'd always recommend making sure you get one that's easy to root, since that allows you to do so much more cool stuff :)