The takeaway lesson here is that it is far easier to create typical T-shirt art using a VECTOR program than a bitmap program. CorelDRAW and Adobe Illustrator are vector programs; Photoshop is a bitmap program, and is just not the correct type of tool for most T-shirt art.
As to which vector program to use, well there are a number of tools that will do the job, from CorelDraw and Illustrator to free open source tools. You can download a free trial of most (all?) of the tools, and that is the best way to see which you prefer. There is no one "best" tool for everyone, as everyone has their own likes and dislikes and ways of working that will better fit with one tool than another.
That said, I have used both Corel and Adobe products since the early 1990s, often with no choice in the matter as the tool was selected by my employer. Both companies have their shortcomings, but personally I prefer Corel's interfaces and business practices over Adobe--only Microsoft manages to piss me off more than Adobe! Hey, but that's me. Try before you buy and see what you like. They will all get the job done once you learn how to use them.
