You say GM=reliable and mention the engine only.
The 103 engine is very durable as well, and if it was maintained, is perhaps among the least likely trouble/cost factors on the car you will need to consider. For example, my motor has never once been opened up, and I am not alone. Runs sweet.
I'm not certain that a 6-year old GM is going to cost you so much less in annual maintenance. Perhaps it will have an advantage for the first year or 2 due to its 'newness', but perhaps it was not maintained either, and history suggests the total expected lifespan is not like an MB.
Look ahead at how long you intend to keep the car, and what it might cost over time in depreciation, repairs, and everything.
Then consider your daily driving experience. You should like your car, at least to some extent.
For a seasonal car, the RWD may not be what you want.
Many factors to consider.
Also remember, this is the place where folks come to complain.
See if you can find a GM board, and see what those owners are griping about. Should prove interesting...
1986 300E 5-Speed 240k mi.