Graphics Pixelated When Uploaded to Web

This is something that would be a dream come true if fixed. I have designed graphics and uploaded them on blogger, wordpress, facebook, pinterest, Zazzle, Cafepress... the list can go on. I've resized them to fit the entirety of the artboard, 1000's of pixels, but they still have that haloed pixelated look. I know it's going to be a simple fix, too.

I am using Ai CC & Ps CC all updated as of 11/21/17.

"ALL CANNOT" was saved as a *.jpg (in Ps 72ppi)

"1. Speak...* as a *.png with a transparent background. 300dpi Ai

Heart with thick strokes as a *png file (that are removed for final) was saved and screenshot'd on wordpress . 300dpi Ai

Thanks in advance!

(Text and Solid Colors--no gradient) (Big heart is how it is supposed to look)