If those are your choices you might want to wait a bit:
- The new Kobo was just announced but its not shipping
- The Sonys are currently selling at list price; wait a bit and they'll start getting discounted once reality sets in
- The rumors about Nook2 are still out there
More importantly, the business is in pretty big turmoil right now and prices will be in flux for at least another year so if you're not going to get good heavy use out of the reader right away it is best to wait.
Best guideline I know for when to buy electronic gadgets is "Buy when it hurts not to".