Stick at illustrator Mark it's really good ! There are good tutorials with in the package itself, or plenty for free on YouTube. Aside that people like Digital Tutors -
http://www.digitaltutors.com/trainin...ator-tutorials or Lynda.com -
http://www.lynda.com/Illustrator-tra...als/227-0.html are all good.
People often over look the training and tutorials that come with the software but it's very good. If I ever get stuck using adobe stuff that's the first place I look. Post anything on here I'm happy to help, or there are plenty of illustrator forums out there.
Corel draw and inkscape are both okay but depending on where you're getting stuck they all work much the same, it's just the interface and short cuts I struggle with on those 2 so don't use them. Illustrator is the industry standard for a reason.