I say iPad with 3G would be good for travelers. I think it would be really good for international travel because with an unlocked phone, data is still really expensive abroad. So if there were good deals in say, Europe, where you could just pop in a MicroSim when you got there and use data for awhile, then it would be handy. Especially since the iPad is unlocked from the get go.
Now for me personally, I can only envision using the iPad at work or at home. Both places I have wifi. If I'm out in the grocery store, shopping, or out at a bar I'm not going to be carrying a huge bag with my iPad in it. I can't really see taking the iPad anywhere else besides home or work, unless maybe to a friend's house and chances are they will have wifi.
Everything I need to access on the go, RSS, email, google, etc is on my iPhone.
Therefore, 3G if you are a traveler, Wifi if you are not.