For gaming: single threaded performance is usually better to prioritize.
For everyday use (web browsers, etc): both, but generally prioritize single threaded performance first. Multithreaded performance is usually already more than good enough on modern chips that have fast single threaded performance.
For heavier workflows: multithreaded performance is usually better to prioritize (particularly on workloads that inherently use a lot of threads). Single threaded performance still matters, but most modern CPUs are good enough on this front.
Microcode is used very heavily in modern CPUs. It has been since the 90s.