My brother bought Wix filters for his two MBs recently simply because it was easier to get them with his work schedule. They appear to be quality filters, and have the correct filter shape and size -- full flow on the bottom for the 603, bypass at the top, full bypass for the 300D.
I still use German filters for the simple reason that they are made in a country where very long engine life under severe conditions is expected. Wix appears to be the best I've seen for US made (if they are anymore, even Bosch is usually India now) filters. However, the expectations are different, even with Wix being a major supplier of farm and over-the-road truck filters.
Unfortunately, the only way to tell would be to do a long term study.
Use what you want, I stick with Mann, etc.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!