[metallicpea]

1st, not the xdrive.

After that, the biggest question is how long are you going to keep it? If only a couple years, get the M3, it's value is down and if you get a nice one and keep it nice you will do OK when you switch next, the 435, not so much.
If you might keep it awhile, you have to decide if you want the upkeep for a possible future collector like the V8 M3 (they have engine rod bearing issues I believe), or a more drive and sit option of the 435 that you dump at low value as soon as it starts giving you trouble.

Just because we have some disposable income doesn't mean we need to dispose it. As cars are changing so drastically now, there are some cars you can own, enjoy and not throw money out the window in the long term. The M3 might be one, but it likely wouldn't be trouble free.