I'll give my current top 15 because there's a few extra I think deserve a honourable mention at least.
1. Cofagrigus
2. Reuniclus
3. Numel (If I ever had a real life pokemon pet, I'd want it to be a Numel)
4. Malamar
5. Mawile
6. Dragalge
7. Roselia/Roserade
8. Scolipede
9. Ho-oh
10. Starmie
------Honourable Mentions------
11. Sigilyph
12. Ampharos
13. Pumpkaboo
14. Darmanitan
15. Tyranitar
Honourable honourable mentions: Gengar, Magnezone, Lapras, Togekiss, Trevenant, Galvantula, Golurk, Flygon, Scrafty, Gulpin, Seviper, Tropius, Squirtle/Blastoise, Torchic/Blaziken, Swanna, Kyogre, Conkeldurr.
As for my favourite types...(in no particular order)
Poison, Ghost, Water and Psychic are above the rest. I often find I have pokemon of these types in my first team without actively trying to add them.