Heh, my favourite always changes...it could be Kingdra then suddenly Machoke. (These are not my favourite by the way, just examples.) Usually I make mini groups for my favourites like 'Starter favourites', 'Non-Legendary', 'Baby favourites' ... I'm sure you get the picture. But I'll only list two groups, it's easier.
At this moment in time it is in the list of:
Non-Legendary
1. Breloom
2. Ampharos
3. Flygon
4. Umbreon
5. Espeon
Legendary
1. Suicune
2. Lugia
3. Rayquaza
4. Regice
5. Mesprit
I think Suicune is the only one on that list that has never moved from the spot it is in currently, and to be honest I don't think it will. Out of them all...Suicune is my favourite with Breloom close behind it, then Ampharos and in fourth Lugia.