My favorites are Garchomp, Luxray, Floatzel, Infernape, Torterra, Cranidos, Lucario, and Leafeon. Flygon used to be my favorite non legendary Dragon Type, but Garchomp easily took its place. I fell in love with it after catching my first one and still add it to nearly all my teams. There's not much I can complain about Garchomp really. Not to mention Cynthia uses one and she's my favorite Champion. The same applies for Luxray, it's one of my most reliable battle partners with a cool design and everything. Not only is it my favorite Electric Type, but it's become my #1 favorite Pokémon overall.
As for Floatzel, the design and personality it seems to exude is what caused me to try training one back in D/P/Pt and there's no regrets. It's one of my favorite Water Types, although when making RP characters I do like making its personality into the more villainous types. Buizel was also rather cute, so that's another plus in my book. Infernape was the starter I chose when I first played Diamond and later Platinum. Besides Lucario, Infernape is one of my favorite Fighting types because of its ability in battle and design. With Torterra, it was the first Grass type starter I trained before the fifth gen. Like Infernape, I like it because of how well it does in battle and design. In Pokémon Battle Revolution, it was on one of my first teams.
Cranidos and Leafeon were both firsts for me, since Diamond was my first handheld game. Also, Leafeon was the first ever Grass type I trained, which I've also come to love. Cranidos was the first Rock type. Both of them have great designs and I definitely like Leafeon's battle ability. It was surprising to see how well it did in battle, especially considering Grass types are not very high on my list of preferred types. Teaching it Leaf Blade was definitely a highlight, considering that's one of my favorite Grass type moves. As for Lucario, well what can I say besides it's just an awesome Pokémon lol.