Here are some reasons I think Pinkie Pie is better than Rainbow Dash.
1. Pinkie Pie doesn't tend to show off or brag about her accomplishments.
2. Pinkie doesn't care about being cool. She just wants to have fun.
3. Pinkie will go out of her way just to make somepony else happy while Rainbow is just in it for the glory.
4. Pinkie sings more and has a prettier voice. (Who cares if she sometimes does it randomly out of nowhere?)
5. Rainbow Dash can be a little bossy to Fluttershy while Pinkie just tries to help Fluttershy out of her shell in a cute, cheerful way.
6. Pinkie Pie is so random...and that's part of what makes her so awesome.
7. Who saved everypony from the parasprites? Not Rainbow Dash.
8. What's a better reason to celebrate Nightmare Night? Play pranks to scare ponies or go door to door for free candy regardless of your age? I'd go for the free candy.
9. Pinkie wouldn't try to solve dragon problems or any kind of problem with violence. Remember when Rainbow kicked the dragon in "Dragonshy"?
10. Pinkie wouldn't make fun of Twilight for being an "egghead".
Now, just remember, this is just my opinion. I'm not trying to get you to like Rainbow Dash less. I'm just trying to get people to respect Pinkie Pie equally. I know, after reading this, some of you may wanna name 10 or even 20 things about Rainbow that make her better than Pinkie. But, don't even start! I don't wanna cause any conflict here. I'm just giving my honest opinion. That's all. So, please, don't be mad.
Thanks for reading. :)