Difference between tile notifications: big white number on tile vs little black circle?

[mildor]

What's the difference between this two types of nitufucation?

The big number on the live tile (in apps like messages or mail)
And the little black circle in the top-right of the tile...

I like more the first one, but... they appers randomly? or its the app?

 

[BenJAMIN_2009]

It depends on the app developer like wpcentral lets you choose but some don't just depends on aesthetics I guess