I love both a lot but if you look at their stats and type advantages Leafeon is better. Sorry Glaceon even if you would easily beat Leafeon, Leafeon could beat more than you. You don’t suck just that Leafeons a bit ahead of you. Don’t feel bad beat some dragons!
Despite both being adorable, in game Leafeon is stronger if you don't rely on Glaceon's Frost Breath, ice types seem to be more frail in general compared to grass types although in a battle Glaceon would most likely beat Leafeon. Therefore as much as I love both Leafeon will have to get the vote from what I experienced when using both together.