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Stage-weighted multiplies each open deal by its stage probability. Judgement asks the people closest to the deals what they commit to. Historical extrapolates from past periods and conversion rates.
Each is defensible. Each is wrong in a characteristic way, which is why running one alone is the mistake.
Stage-weighted inherits your stage discipline: if deals sit in optimistic stages, the arithmetic is precise and wrong. Judgement inherits the forecaster's bias, which is usually consistent and therefore correctable.
Historical fails when anything changes — a new product, a new market, a new team — which is exactly when the forecast matters most.
None reliably. Running two and examining the gap beats optimising one.
Per stage. Per-deal optimism turns the forecast into a negotiation.
Store submissions immutably and compare them with actuals over several periods.
Half an hour with your own data usually saves reading three of these. The guides will still be here afterwards.