Some of the reasons for my preferences:
Adobe's insistence on limiting Illustrator artboards to 227" is detrimental to them "conquering" the signmaker market, in my opinion. The ability to create works at 100% (which Flexi and Corel will do) eliminates that problem. Using Illustrator and scaling is fine if I'm doing it myself, but if someone else makes it and I'm given the wrong scale- aye-yi-yi.
For kerning, I find CorelDraw and FlexiSign to be much easier to adjust. Maybe it's because I'm not looking at the correct tool or in the right place in Illustrator, but being able to just click on an individual letter and "drag" it a bit in one direction or the other is easier (as Corel and Flexi will do). And if anyone can tell me how to accomplish that in Illustrator, I will love you forever!
Creating dimensions in both Corel and Flexi is- well- not necessarily easier, but it also doesn't require I buy a plugin, either. The function is built into the programs.
Strokes and fonts... ugh! Not really related to discussion at hand, but I recently had a customer that wanted a template so they could create their own printed paper inserts for some changeable signs. Fine- we'd turned a nice profit making the initial signs- and they're still buying other stuff from us- so I created their template. Except the font they insisted on for their signs can't be embedded in a PDF due to licensing restrictions.
The conversation went something like "What? Can't you just give it to us?"
"Well, sure. I can send the font file and you can install it on the workstation you'll be using to create the inserts."
"Unh (tooth-suck noise)- just make it part of the PDF."
"Well, as I said before- it can't be embedded because of licensing restrictions."
(Tooth suck noise again) "You're making this too difficult."
"May I suggest you use Arial Narrow? That's close enough."
"But it's not our font!"
Eventually, I renamed Arial Narrow with their chosen font name and embedded it. They haven't noticed.