The original iPad featured EDGE + Triband HSPA connectivity. The second generation iPad was then released with Edge + Quadband HSPA. Now the new iPad 3 features 4G LTE; UMTS/HSPA/HSPA+/DC-HSDPA; GSM/EDGE.

Take a look at the video below to see their network speeds compared.

Update:
For those wondering in the comments, these tests were performed one by one (no interference) in the exact same spot, with the exact same SIM, against the exact same server. The carrier was Bell in Canada.