The Lexus LX and GX are the most reliable of the three by far. The Mercedes will have the most problems and be the most expensive to repair. The Mercedes will drive better if you are looking for better handling. The LX and GX are about the ride comfort and towing capabilities. You get more car for the money with the Lexuses.
I would recommend the Lexus RX350 or RX450h. These are more attainable for your budget and are not overkill for your situation, like the GX and LX are. They are also very reliable. They don't fit as much in the trunk, but you didn't say you wanted trunk space. The LX is huge and a gas guzzler. The GX is a much more comfortable Toyota 4Runner.