They’re extremely different characters, the most they have in common is maybe the arrogance but epic!Gil is more “overconfident schoolboy” and is often even respectful vs FateGil’s supreme arrogance. CanonGil is full of false bravado, is openly a softie and a romantic, gullible, not very smart, and cries easily. Enkidu is the wiser and more knowledgeable one, and is his advisor.
Tbh I don’t like ArcherGil much and haven’t rly bothered to read any of the Fate crap he’s in, but I do like CasGil a lot even if he’s still virtually a Fate OC bc his love for Enkidu is front and centre and that sad gentleness blends with his new mellowness and maturity really beautifully. He’s also super moe