Haven't been to any of the breweries so I can't comment on the tours/facilities. But as for the beer itself, of the three listed above, I would rank them 1.Buffalo Bayou > 2.Karbach > 3.St Arnold. However, I'm a recent transplant to the area and it seems that St Arnold has a pretty strong local following, likely because they're the largest and have been around the longest.
The best beer bar I've been to in Houston is The Hay Merchant. Huge tap selection, all good stuff. If you want a hidden gem, look up Moon Tower Inn.
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