DSF

For us, it needs to have full ICC colour management and Pantone support being useful too, along with being the industry standard it helps when we're printing for other designers. There's plenty of free and paid for tutorials on the internet including good walk through videos on YouTube.
We don't tend to go by price alone, and certainly don't buy the most expensive thing for the assumption that it is therefore the best, but seek out what is best for us to do the job, and so for us that means we need Photoshop, which is £7 per month, so very easily to budget for.

I'd imagine the best is the one that suits you and your needs and that you find easy enough to use, that is until someone shows you something that another one does that you can benefit from and find that you then can't be without.
Mark