I confess that I think there is nothing to beat Adobe Photoshop when it comes to pixel based image editing. However, it might be considered expensive; it will cost you just on £18 a month for the single app, which is beyond the range of some, and discourages others who don’t like the subscription model.
Version CS6 (Creative Suite) can still be purchased from third party resellers for a one off fee, but it hasn’t had a full feature update since 2012, and is gradually being left behind by the much updated CC (Creative Cloud) offerings
There are, however, alternatives. There’s the free GIMP (GNU Image Manipulation Program) that is very powerful – if not that easy to use. Still, if you are willing to put in the effort, GIMP is an extraordinary piece of free software.
For the Mac user, Pixelmator is a full featured (their words) picture editor which only costs $30 or so and might well be worth looking at; I’ve not used it, but have heard good things.
Adobe Photoshop Elements v14 is a cut-price, cut-down version of Photoshop aimed at photographers. It is surprisingly powerful – using much of Photoshop’s code – and is a one-time purchase for around £75. It is available for Mac and PC. It utilises many of the Photoshop filters and has good text support.