I actually have changed my mind about my favorite being Giratina. I have a newfound respect for Dialga, and it is now my new favorite. Not only is it cool in appearance, but it also is resistant to 10 types of attacks, has only 2 weaknesses, great defenses, and a whopping 150 base special attack. It is also somewhat fast with a base speed of 90. It is also of the dragon type, which is more than half the reason why I like it.
Of course, I'm not saying Palkia is bad or anything(It's also a great dragon pokemon, having only 1 weakness. However, it has less resistances.), but Dialga seems to be the superior dragon in my opinion.