Firstly I count myself very lucky to be able to enjoy and have the means for both fine vehicles.
BMW always has done a pretty good job with the 5 series. Together with the 3 series there bread and butter and certainly most 5 series are build in Dingolfing main plant in Germany. I always as a kid liked the understated yet capable 5 series including the M5, so once I had the money I got one and I loved the way the diesel pulled and sounded. Got it in Msport dress (nicer wheels, sportier suspension, much nicer steering wheel) with comfort seats and 360 surround view, soft closing doors, bunch of packages. Been trouble free except for the DPF...
Since I understand engines pretty well and I researched after purchase (I had moved back to the US, was in a hurry and it was more of a passion buy without proper research...) I would say the DPF and urea NOX cat systems are cancer to modern diesels. Great when new but all those crazy high temps during regen (1600 degr F exhaust temps which the turbo and engine room is exposed to as well) are cancer to the plastics, wiring and go together with fuel dilution, early turbo and bearing failures, urea metering valve plugging etc etc. No end to the potential issues of all these complex systems. Basically one big old mess. So when the dealer idled a near full tank of diesel out of warranty and plugged the DPF I went for a DPF/Urea/NOX cat delete and tune. This also keeps the EGR closed so no more soot build up in the intake manifold. Been absolutely amazing since. Awesome increase in power (258 to around 320) and torque (from 413 ft lbs factory to now around 530), about a 10% increase in MPG. The exhaust sounds like engine angels in heaven
Like this, 0:15 onwards. Turbo whistle included. Inside equally quiet with the windows closed, which I like. I have had a colleague with an M3 who was jealous (and probably nice to me as well...)
P.S. I sometimes wish this straight six diesel is in the 200 series. Perhaps 4 liter with some more HP and torque. That would be heaven. But hey, they would have to supply with the emission system and kill the reliability.