Most people have different preferences for what programs they like to use.

Here's a list of some online and offline programs you can use:

https://wolfplaygame.com/forums.php?f=35&t=10523

Personally, I wouldn't risk using an online art editor on the offhand I forget my log-in information or the website goes down or becomes unuseable

From what I've heard though, pixlr is a decent image editing website..