Evan as an amateur, I do like to have a selection of programs available to me. I think that it is a case of having the right tools for the job and, usually, one is not enough. My graphics programs consist of Photoshop Elements, GIMP, Clip Studio (formerly Manga Studio), InkScape, Artrage, PostWorkShop Pro 3, Poser, and Carrara. I know that 3d software is a little frowned on for covers but it can be very handy and, in any case, I work hard to ensure it doesn't look like 3d.
I don't think that it is enough to have just the right tools though - the right resources are just as important. I suppose my biggest bugbear in book cover design these days is the use of fonts. Not just having the right fonts but also having software that will allow to work with it properly (GIMP is actually rather good at that now).
Of late, I have been experimenting with re-creating the look of pulpy mass-market paperbacks. This means a work flow that largely consists of Poser, GIMP/PSE, Artrage, and then back to GIMP. I'm a big advocate of Artrage as it can do a fantastic job of turning a 3d render or photo into a faux painting - it's not an automated process though, so you do have to do the work but it produces the right results (and has the virtue of being much cheaper than Corel's Painter and much, much easier to use).