Only the Kindle 2 is available new. On Amazon a used K1 is about $290 vs $359 for the K2. The K1 would have to be significantly cheaper to make it worthwhile, but you might find it cheaper in your area.
Both give you access to the Kindle store, and both read exactly the same ebooks. The K2 has more greyscales and TTS (text to speech) and many minor improvements which taken together are significant, but the K1 and K2 are in many ways interchangeable. I don't intend to upgrade from my K1 to a K2, but if I was buying today I would get a K2.
As JSWolf suggests, there are many choices other than a Kindle - see
E-book Reader Matrix. Absent a particular feature you must have, a Kindle is a good choice for a new reader of ebooks in the US.