I switched at the MMX era, not because of the bug (it was fixed prior to that) but because then OEM prices were falling.I would have to say early Pentium chips with the FDIV bug and/or the f00f bug were probably the worst. Think about it, we're talking about a CPU that screws up floating point calculations due to a design flaw and can be locked up to the point of requiring a physical reboot with one malicious instruction. I stuck with 486 chips until the Pentium II era.
https://en.wikipedia.org/wiki/Pentium_FDIV_bug
https://en.wikipedia.org/wiki/Pentium_F00F_bug