Depends on numerous factors. In addition to the ones you listed are things like a) to what extent you want to build wealth, b) how concerned you are with financial security, and c) what other kinds of funds you have besides pure cash.
I'd say more is better; I prefer 6 months of cash available. Any more than that, and I'd suggest putting that money to a lot better work: bonds, stocks, business ideas, real estate, etc.
I've got around 4 months of cash handy, but in terms of liquid assets, I could easily go many years without any external income.