Hobby is actually much closer (about 40 minutes away), while Intercontinental (Bush) is about 90 minutes from the port. The other kicker is the cost of getting to and from Galveston from there ... it can run close to $200/pp r/t.
Southwest, AirTran, JetBlue and now Frontier are the major carriers that serve Hobby. American and Delta also have service, but it's very limited. With all but Southwest and JetBlue, you'd have to arrive the day before the cruise, since flight times don't coincide with the ships' departures.
We live in Houston, so we're pretty familiar with what's available, since friends fly in all the time to cruise with us. Have a great trip!
Al