The B58 and B48 are quite impeccably good engines, both in terms of reliability and also performance/response. I had an excellent experience with my B58-powered M240i. I've also never heard anyone needing to do anything in practice with timing chains on these engines, even at high mileage. It seems the whole car would be worn out before the timing chain wears out, provided you use decent quality oil and don't neglect oil changes.
The older N52 engine is also very solid and reliable, my high mileage 2006 330i (E90) has been rock solid reliable in its powertrain.
My mechanic told me the N20 engine is terrible though, he has encountered an absurd number of them failing. The N54 is solid enough mechanically, though they get HPFP issues and need occasional cleaning of soot/gunk from valves.
The older N52 engine is also very solid and reliable, my high mileage 2006 330i (E90) has been rock solid reliable in its powertrain.
My mechanic told me the N20 engine is terrible though, he has encountered an absurd number of them failing. The N54 is solid enough mechanically, though they get HPFP issues and need occasional cleaning of soot/gunk from valves.