I briefly owned a 97 528. Nice car. Sold it to my neighbour, and she loves it.
It's a very different animal than an E420. It's a nice six cylinder sedan, but is pretty tame compared to the V-8 Mercedes.
One thing I really found odd in the BMW was the ACC that required a manual engagement of the compressor. Weird. Maybe I was doing something wrong, but that seemed to be the way it worked.
As to W124 (92-95) vs. W210 (97+) V-8 MB's, personal preference is the key. The 97 has the "four-eye" front end, which I find very attractive. The 97- also has a steeper final drive and five-speed automatic. The W210 E420 is a pretty quick car, right on top of the 540i.
The W124 has a little more dated look, but looks "MB" in the classic sense. It also suffers the 2.24 final drive that saps alot of it's get up and go, but makes it a superb highway cruiser. The interior materials are a bit better in the older cars, but they do lack some modern touches, including side-airbags, keyless entry, and ESP. The AC in the later cars also blows colder.
The BMW will not hold it's value as good as any of the MB's. I didn't own the car long enough to even do an oil change, but I think the six has a timing belt as opposed to MB's double row chain drive. The belt requires more frequent service.
But, the BMW will be much less expensive to buy compared to a 97 E420. I don't know about your home market, but in my neck-o-da-woods, a 97 E420 sells in the $45-48K range, and a 97 528 in the $30-35K range.
With any year E420, you'll probably be happy...
1998 C230 "Black Betty"