I have more experience with Home Depot than with Lowe's, so I can't really say which is better, but I prefer our "local" chain, McLendon Hardware. (Local in quotes because it was bought a year or two back by someone in Tennessee.) After the buyout their employee took a deep nosedive, but it seems to have recovered to where they're somewhat better than HD.
I'm not a fan of boycotts based on other people's personal opinions or spending habits. Though I was raised to boycott nonunion lettuce.