Leopardmon X and play out a leopardmon ace for free, which can go into another X.
This deck has 20 cards playable by Leopardmon X
It has a high lv6 count but its able to player them out fairly easily, so it doesn't slow it much. MedievalGallantmon can be free off Leopardmon X, and Zephagamon Ace can be played for 1 memory off Leopardmon X. And this deck leaves plenty of lv5's for blast evoing. Also with 18 lv6's theres about a 75% chance of finding one to evolve to for free off Mametyrnamon. Though using Tortomon's inherit effect to evlove to Leopardmon BT13 is still typically the best play.
Using namakemon to suspend itself and search, then evolving a megakabuterimon ace on it for a uneffected ace target is very strong. though you can also suspend Megakabuterimon by Medievalgallantmon's on play, aliance, digisorption, or through Zephagamon ace's effect for the same defensive play.
Dinomon is also tempting but I couldn't find space for it. A Leopardmon BT13 or two could be cut for it, but I think playing 12 Leopardmon's just sounds more fun
Finally I prefer the searcher options over a more consistent number of Lv3's and Lv4's because this deck wants the stored memory to combo off with, and searching for Leopardmon x can be fairly important. Once the deck gets started you typically wont need to stack from the breeding zone very often anyway.