TheNoobHolocaust on 12 November 2011
1. Assassin's Creed II
2. WWE SmackDown vs Raw 2010
3. ICO
4. Uncharted 2: Among Thieves
And as soon as I finish both Uncharted: Drakes Fortune and Uncharted 3: Drakes Deception on Crushing I'll get Platinums.
Also to answer the question in the OP I went through my whole trophy list and GTA IV stuck out for me, I finished the game with both endings and still only had 1%, so I'd say thats probably one of the hardest games to Platinum.
