tough call there.
both of these toys are very good TFs, and their features justify their prices.
for Energon Megs (assuming you get the leader, not the deluxe version), you get an excellent homage to G1 Galvatron, a cool-looking jet mode,plus an additional tank for free.
for Galaxy Force, you have a triple-changer with a wicked personality. though i'm not much of a fan of his batmobile mode, and there are reports of stability issues with this (which i don't have with Cybertron supermode OP).
depends on what show you're a fan of, as well as the features you're looking for. both are excellent toys, and ultimately it comes down to alt-mode/homage preferences.