Here's my take: which software will work for you is going to depend on how much editing you want to do, how software savvy you already are and what kind of edits you want to do. For instance, as TiredIron points out, Photoshop CC and Lightroom are the industry standards. But if you have little to no experience doing photo editing (and my guess is, that's the case) than even with all of the instruction out there, you'll find them overwhelming. Same with GIMP--it's free but not easy to use if you're brand spanking new to this.
I think there are really two issues/challenges here: managing your photo library (both when you initially download your files to decide which ones to edit/keep and which ones to...meh) and then for editing itself. And not all software excels at both. Which computer you have/OS you use has a lot of impact on how you organize/display/choose to upload your files.
Affinity Photo was designed for Macs and is supposed to be an alternative to Photoshop CC. I'm very impressed with it. It will cost you about $49 and then you own it outright. If you have no background with editing, then the execution and details around layers will likely through you for a loop and it may be too advanced for you. And yes, the Adobe options (Photoshop CC and Lightroom) are the industry standards. $10 a month doesn't sound like much but here's the rub...you aren't going to use it for just a few months or one year are you. If you lease them and keep editing for 3 years that's $360 (and more with each year). If all you're looking for is software to sharpen, delete a few water or dust specks, maybe saturate colors, then you've got lots of free and cheap options. With a Mac, you can use iPhoto or Photos to do all of that. A simple program like SnapSeed (which I believe cost me $10) could do that stuff. Picasa is free (but will be losing support). The Nikon Picture Control Utility software will convert from RAW and do basic functions while also helping you manage photos.