C-alkylation vs. O-alkylation

canion effect:
Li, Na, K, Cs
C---------O
smaller canion like Li can chelate with Oxygen, so carbon is more active compared to the oxygen atom. But at the same time, both C and O are less reactive compared to bigger canion!

solvent effect:
hexane, toluene, THF, acetone, DMF, DMSO
C----------------------O
substrate is less solvated in less polar solvent.

temperature
high temp seems favor O alkylation.

leaving group
OTs, Br, I
soft leaving group favors C-alkylation.