They both can achieve the same end result, the difference is how you get there. AI is the design industry standard, so there is more information available via design forums and tutorials for Adobe products.
Having said that, I believe Adobe is changing how they handle licensing and upgrades, while i'm not completely up to date on it, I think the overwhelming opinion was negative.
I use Corel Draw x4, because it is the industry standard in the engraving industry (we started in engraving before signs) it's what i'm comfortable working with and i VERY rarely get sent a file that I can't open, and if I do, i just contact whoever sent it and ask for a downsaved version.