DEFINITELY either Chicago or Vancouver! They are both truly world-class cities with great art, culture, food, activities, nightlife, etc. I recommend living right downtown in the heart of either city for someone in his situation to make the most of the experience.
Vancouver is more "international." It offers and outstanding variety and number of outdoor activities nearby and is very good for people who like to hike, bike, paddle, ski, etc. The climate is more moderate in the summer. Being all the way on the west coast it is not an ideal hub for visiting the rest of the continent. The Canadian dollar is considerably weaker than the US dollar so money will go further in Vancouver if that matters.
Chicago has more people in the metro area. More people in Chicago speak English as a first langauge than in Vancouver (both total numbers and percentage). Chicago is a good hub for visiting the rest of the continent. It can be pretty hot in the summer, but if you can get out on the lake it's nice!
Cleveland is OK but it is "just another city" and not anything remarkable. It is certainly not on the level of Chicago or Vancouver (though of course it is also less expensive). Pittsburg is what I would describe as a city in decline and I really can't think of any reason to recommend it.
Just my opinion!
[This message has been edited by Lud (edited 09 January 2003).]