If I was to guess now I'd say Hamilton.
Testing next week will show who's improved and who hasn't. I got a feeling Ferrari haven't gained as much as is being said.
I hope McLaren will improve but that's a bit off topic, I can't see anyone other than a Merc driver winning since the rules have barely changed and Merc have been so dominant. Nico had the best run of his career at the end of last season, turning that into a title winning season is another thing.