Gateway is a newer/nicer larger property. It's got direct access to metro. If you're trying to stay in Arlington, but not necessarily in Crystal City, check out the Key Bridge Marriott. Gateway's a little more modern, but the service at the Key Bridge is stellar. In the Crystal City area, there are several Marriotts (Courtyard, a great Residence Inn, & an Ritz, but I've never been to the Ritz or to the CY)