Photoshop

[Baniwell]

CS6 - the best of the best!

 

[Truxgo Guy]

Paint Shop Pro from Corel is not bad as a starting point.
Otherwise, specially if you're looking for something free or open-source, GIMP would be the best option to go.

 

[spinservers]

Another +1 for PhotoSpace

 

[kevinsimmons]

Photopea,Pixelmator Pro , but photoshop has the best.