I'm not sure that I understand the need for another thread... but ok.
I have an HP 6122 - which is one of the latest generation of HP printers - that I won in a raffle at work. And I have the i950. It's no contest. I bought the i950 because I wasn't pleased with the quality of the photos, or the drivers, for the 6122. But the 6122 is supposedly a business printer and doesn't take the photo ink so it's not really a fair comparison.
I have personally compared the output of a 5550 with an i950. It wasn't blind or double-blind (everyone knew which printer produced which photo) and they weren't the same photo and were taken by different cameras. I thought the i950 was better and the majority of our judges (my co-workers) agreed.
That said, quality is a subjective thing, and I thought the 5550 did a very nice job. I know the owner of that printer is pleased with it and likes it, and in fact, thought that he couldn't tell that the i950 was better or worse. But the majority thought that they could. Regardless, the latest batch of HP's do print very well and it takes a detailed inspectation to decide which is better.
The droplet size that makes up the "pixels" on the paper is half the size on the Canon i950 (2 picoliter vs. 4 picoliter on the 5550/7550). This should result in better detail. And another fact is that the Canon is the decidedly faster printer. From what the 5550 owner said, it appears that the i950 prints about twice as fast.
For what it's worth, I'm not really advocating that the i950 is the best printer. I'm not saying, "it's hands down better than the HPs", or the Epsons, or Lexmarks, anything else. About all I can say with certainty is that I wouldn't recommend the 6122 as a photo printer, and I am extremely pleased with my Canon i950. I also think that many of the other printers out there do as good a job and that it would be hard to get much of a dud of a photo printer from any manufacturer's latest photo printer line.