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$$\mathrm{Primary}\gt \mathrm{Secondary}\gt \mathrm{Tertiary}$$ (alkyl groups donate electron density via +I effect and destabilize the negative charge).
Stability also ↑ with $$-I$$ substituents and s-character: $$\mathrm{sp}\gt \mathrm{sp}^2\gt \mathrm{sp}^3.$$
