Remember the old advertising jingle: Wouldn't you really rather drive a Buick? Many people would.But until the introduction of the 2004 Rainier, GM's near-luxury brand had nothing to offer buyers who seek a mid-size sport-utility vehicle.The Buick Rainier seats five and boasts an engine powerful enough to pull a boat or horse trailer. The Rainier shares its underpinnings with several other mid-size GM SUVs, but it alone offers a V8 engine in the standard-length wheelbase configuration.The others offer the same V8, but only in their extended vehicles that come with three rows of seats, namely the GMC Envoy XL and Chevy TrailBlazer EXT.