Car and Driver is my all-time favorite.

I find Motor Trend to be a good one, too, but for different reasons. They usually do good comparisons before C&D, but ever since C. Van Tune left them, I've found the articles to be written for a different public. Not my cup of tea.

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2008 ML320 CDI | Iridium Silver | Black ARTICO Leather | Premium Package (H/K Logic7, Parktronic, Rear Heated Seats, Rear Power Hatch, DVD Nav, 10-way Front Seats w/ Memory) | Backup Camera | Aluminum Running Boards | 4500K MTEC Low-beam HID | 30% Metallic Tint | Boomerang2 Recovery System | Weathertech Front Floorliners | Bridgestone Blizzak DM-V1 Winter Tires