What is the worst possible processor to date?

Answer 1

To judge a processor as "bad", you have to ignore their performance relative to the newest ones on the market. Processors improve all the time, so just because one is older, slower, and lacks as many features as newer ones does not make the older one necessarily bad, just obsolete:

The worst processor in terms of quality control was probably the earliest editions of the original Pentium processor. These processors contained two infamous bugs. One was the f00f bug, which was a faulty instruction that could easily cause the processor to crash under normal operation. The second is known as the FDIV bug, which caused significant (though statistically uncommon) errors in floating point calculations. Intel replaced these processors free of charge for the lifetime of the processor, and the flaw was quickly fixed.

All VIA C3 processors offered performance less than half of that of a Pentium III at the same clock rate. The VIA C3 was meant to compete on power efficiency and heat output, not performance, so this may not be an important failing.

Later models of the Pentium 4 had a performance equivalent of an AMD processor with 2/3 the clock rate. Basically, the Pentium 4 needed an extra GHz to match an AMD Athlon 64 in performance.