I will assume that ptshirts means what software is used to prepare artwork in an embroidery shop as opposed to digitising the artwork for use on an embroidery machine.
If you mean artwork preparation then of the 2 mentioned the short answer is Illustrator, but a lot of embroiderers I know (myself included) use COREL Draw for artwork preparation. Both CORELDraw & Illustrator provide vector based artwork.
Most, if not all, embroiderers would accept image files in JPEG, BMP, PNG etc as artwork for digitising.
But, if you meant what software is used to digitise the artwork (convert into a format an embroidery machine can read), you need a digitising program...of which there are many on the market, Wilcom, Capital, Pulse, Sierra, EmBird etc ranging in price from a few hundred dollars to many thousands of dollars for a top of the line program.
The digitising software you choose depends on what type of design you are mainly going to do...if you are going to be doing mainly corporate logo or clipart type work a basic digitising program would probably suffice.
If you intend doing more complex designs with colour blends etc then a higher level software would be better.