The C180 doesn't have a great reputation. They are not exactly reliable, it's auto and it's from an era of Mercedes where their galvanisation processes were laughable. The other is one of the last bulletproof Volvos made with one very reliable euro3 diesel lump. They do not rot and they do not go wrong. I think I'd pass. The Merc has it on looks, of course because it's a sporty saloon, not a man's man estate. But that's it.