You have the budget to purchase either a Japanese or European car...

But do you have the budget to maintain the European car for a long time?

Merc and BMW will have a higher yearly maintenance cost compared to Japanese brands, and their spare parts and yearly insurance cost are higher too.

Find out the following,

1. Service Cost
2. Service interval
3. Spare parts cost for common items that can fail during 5 year ownership (or 10 year depends on your planning)
4. Consumable cost (Tires, air-con filter, engine oil etc, some of these items are included in 1. Service Cost).
5. Insurance
6. Road Tax

You could find out by simple googling, forum, service center.