I'd definitely go with Midnight Club: Los Angeles. Fast, fun and styIish.
Its also a colossal pain in the neck to play. Its nice that the game has no boundaries but it barely has any structure either.
That's exactly what's so great about it. Midnight Club invented open-world racing and it's the only series that actually utilizes the open-world design. If you want closed-off tracks there's plenty of other games to choose from.