Personally I'd stay away from both. In my opinion they are overpriced and primitive. We have both Signlab and Flexi here at the shop. The only people who use them are old timers who have been using them for years and years and can't wrap their head around a new piece of software such as Corel Draw or Adobe Illustrator. I guess I could understand if you were doing ONLY vinyl cutting why you could want signlab or Flexi but if you are designing also...why waste the money?
So, you think Flexi's RIP is primitive compared to Corel's and Illy's? Oh wait, those programs don't have RIPs.
It really depends on what you're going to be using the software for. If you're strictly cutting vinyl, then pick up a used copy of Corel, grab CoCut and go at it. If you are driving a large format printer, then Flexi is a fine program. It really helps to be able to design, set up contour cuts, RIP, print and cut from one app. I've read others' problems with trying to set up contour cuts in Illy and Corel to send to third party RIPs, etc. In our shop, Flexi is an integral part of a time-tested, efficient and extremely successful workflow. I also use Illy and Photoshop in certain instances, but Flexi is my go-to app.