I haven't used ImagePrint in a while - I've been printing on Canon recently, currently a Pro-2000, and highly satisfied with what I get out of Lightroom, especially with Canson papers that have the custom media configurations.
I haven't tested the same Canson paper with and without the custom configuration file. The only fair way to do that would be if I owned high-end profiling hardware. The Canson profile is made assuming the custom media settings, so using it with a Canon media setting would be a mismatch. I HAVE tested Canson Platine (my present favorite) against comparable papers (notably Hahnemuhle FineArt Baryta and PhotoRag Baryta) that use a Canon media profile, and I like the prints on Platine better on just about every image (it's subtle, but it's there). I don't know if this is "Platine is more to my tastes" or "the media configuration makes a difference"?
When I DID use ImagePrint was years ago, printing from Photoshop to older 17" Epsons (it was once fairly reasonably priced for 17" printers and below), and it certainly made a difference then! It was night and day, whether against paper manufacturer profiles or what I was able to create with a (fairly early) ColorMunki or a borrowed iOne Pro (original). I went to Canon when I bought my first 24" printer, a Canon iPF 6100, and there was no IP for that printer. I've owned one Epson (a 7900) since then, and I didn't buy IP for it because it was so expensive that I decided to try straight from Lightroom first - I got excellent results, and that's been my workflow since.
I have continued to read IP reviews and look at samples when I get the chance, and I haven't seen anything to suggest that it has the kind of advantages it had back when I used it regularly - IP hasn't gotten worse, but other ways of printing have gotten a lot better. I took a good look at samples about 5 years ago, when I bought the Epson 7900, since I could have had ImagePrint for that (for a king's ransom). I didn't see a huge difference then, even in samples ColorByte (makers of ImagePrint) provided. The prints were certainly subtly different, but I sometimes preferred Lightroom, other times ImagePrint - it wasn't like it had been several years earlier, when ImagePrint won on every image, and it was often not subtle.
I have never used QImage on my own systems - I'm a 34 year Mac user (my first Mac was an original 128K) who's rarely had anything else, and I'm happy enough with Lightroom's print module these days that I haven't yet found time to experiment with the very recent Mac version of what's always been a PC-only program. I have used QImage occasionally on other people's systems, and, like ImagePrint, my impression has been "you can get a lot closer in Lightroom than used to be the case".
One of the real tricks that both IP and QImage do that used to be tough to get the Adobe stuff to do natively is output resizing. Both of them resize (and handle output sharpening) on the fly with fairly sophisticated algorithms... Photoshop has always had various resizing algorithms, of course, but they involved saving versions of the image at every size you wanted to print. Lightroom has always had a resize and output sharpen on the fly feature, but it used to be unsophisticated - not much better than letting the printer driver do it (printer drivers just do a nearest neighbor resize - old Lightroom may have been one step better - was it bilinear?).
A few versions back, Adobe bought the PixelGenius resizing and output sharpening technology and added it to Lightroom. They don't offer much control, but the algorithms are excellent. At least in my opinion, it was the addition of PixelGenius technology that made "just do it all in Lightroom" a viable fine-art workflow. Jeff Schewe, one of the brains behind PixelGenius, used to frequent this forum. Once Canon added the custom media types, and paper manufacturers started picking up on that, the number of tricks third-party software had that the basic tools didn't declined again.
That's not to say that a third-party program couldn't do the same things (resizing, output sharpening and custom ink management) better - but they are no longer doing things Lightroom and Canon's driver just don't do the way they used to...