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The Revolutionary War was fought so that we could list the home team second. Don't tell me we fought it for nothing.
There are a few things to keep in mind when planning a trip. If you're flying, some cities are expensive to fly in to, while others are less expensive. Mostly, any route that Southwest flies is going to be less expensive, even on competitors. If they don't fly there, it can be pricey. Trains are a great way to travel along the Northeast corridor, but in other parts of the country they run infrequently, slowly, and can be expensive. You don't want a car in some cities, like New York, because parking and rentals are very expensive.
July 11/12 - Cleveland, Seattle, Milwaukee, Colorado - the parks in any of those cities are right downtown. I wouldn't recommend Kansas City. Since you'll have seen Oakland play three times already, you may want to skip Seattle (though it is a great city and ballpark)
July 19/20 - Definitely Pittsburgh; Boston is also recommended to see a historic field.
Happy trip!