Victini is quite underrated, despite being a "Mew-esque Event". Meloetta is quite underrated as well, despite being an Event Legendary. Bunnelby is quite underrated but it can have the ability Pickup. Plus it can learn a variety of moves.
I see it's best to have something to counter Gliscor's main weakness to Ice. I still say the best Gliscor to use is the one that has poison heal. I consider Gliscor my fav Gen 4 Pokemon even though it evolves from a Gen 2 Pokemon.