Great thread, but nowadays I guess there only a few people disagree on. Milotic, Gyarados, Arceus and Giratina have already been mentioned. I generally go by how the anime pronounces names (unless it sounds super stupid). Generally when I'm talking to my friends about it, we all know each others pronunciations. I think we've got some "Sewy-coon-ee" and some "Sue-coon" going on. Giratina tends to be changed between hard and soft G's at the start which is kinda strange. I've also heard it pronounced with the start as all hard letters -"Ji-Rah-tinah".