I love alot of hacks.
The top contenders for my favourite though, are Glazed, Vega, Snakewood, and Super Rising Thunder (although it never made it past the Alpha stage, what I did play was incredible, and I loved it. Shame it won't be going any further :( )
I LOVE the Fakemon in Vega, and they are all brilliantly designed. If I HAD to pick a number one favourite, it would be Vega.