That question is a bit like asking "What car is best for me" which is almost impossible to answer. In reality, picking a program depends on your skill level. Microsoft Word/Publisher has the capability of producing some very good looking designs with relatively little skill needed.
Inscape [free] is also good, but requires basic graphics knowledge.
Gimp [free] is, IMO, a step up from Inscape, but seems to be a bit more complex and difficult. If you have little to no background in graphics editing, I would not recommend Gimp - you may, however, be able to get away with Inscape with a few hours playing around.
Finally, photoshop [$$$] is probably the highest-end product out there. It is used by a lot of professionals and has a lot of the latest tools, gadgets, and capabilities. It is an incredibly complex program and requires a lot of knowledge and skills to utilize its fullest capabilities.
There are plenty of other programs, but pick what suits your style.