I've been using large format printers for nearly 15 years, and here are some observations (the important unit I've never used is the Canon x300/x400 - I have a ton of experience with the x100 generation, but have only seen occasional output from the newest Canons, never really used one).
1.) Canons ARE lower maintenance - I get exceptional image quality from my 7900, but it does like its nozzles checked. I haven't had a clog a simple clean won't fix right away, but it isn't zero-attention like a Canon.
2.) Epson's current paper feed is far superior to anything Canon has ever put together - it's a straight path that will run essentially any media you can imagine. The 6x00 series Canons have a 90 degree bend in the path, and the 8x00 series actually requires the media to make a 180 degree turn (as well as loading UNDER the printer - not the most comfortable place to load). Even though a 6x00 series Canon looks similar to an Epson, the Epson printhead is mounted at an angle that allows the paper to run through straight, while the Canon printhead is mounted vertically (as in almost any other inkjet), forcing the paper to turn almost 90 degrees in order to run horizontally under the head. This is a real advantage, especially on odd media (I run silk on a backing sheet through the 7900, which I'd never dare to run on a Canon) - even ordinary paper is much easier to load on the Epsons, though.
3.) The image quality advantage of the 7900/9900 over the previous-generation Canons is substantial - you'll notice it every day, on most landscape images. That isn't really a fair comparison, though - the 3880 should be compared to the previous-generation Canons, and the 7900/9900 to the current (x300/x400 generations). 3880 vs. x100 is very close - I have a lot of experience with both, and I prefer different printers on different prints (the 3880 is NOT especially close to printers that use a more recent inkset, despite some claims). I wish I had more experience with Lucia EX as used in the latest Canons - from the test prints I've seen, it's close to the 7900/9900 inks, but not quite there. Canon does have a better blue, due to the dedicated blue ink. The ideal inkset (that doesn't exist)would seem to be based on Epson's newest, but with Canon's extra blue and no-switch blacks. I've never used (or even seriously looked at samples from) Canon's smaller Pro-1, which uses an extra black level, so I can't comment on that. Some technologies are not available in certain sizes - Epson's 64" 11880 is a major generation behind the rest of the line (it's a giant 3880, without the important orange and green inks), while Canon's 9400 uses the current inkset. At the other end of the line, Epson has the 4900, the only 17" printer with a current inkset.
4.)The 7900/9900 are beautifully built machines (in a way that Canons and the 3880 aren't). It's like looking at a Hyundai (3880) versus a Toyota (Canons) and a Mercedes (7900/9900). I haven't really used 44" Canons all that much (enough to know that I don't like the paper feed, but not the hundreds of prints I have on the others), so I am not sure how much better than the 24" machines they might be built. Canons also have the unfortunate sub-tank system that means the big ones really can't be moved once the ink's in. I think the 6400 now has this issue as well (the 24" machines used to not be an issue).
5.) Match your printer to your camera! A 24" printer wants at least a 24 mp camera, ideally a 36 mp camera. 44" printing really requires 36 mp or more. Conversely, only a 24" or 44" printer will fully utilize the resolution of a high-pixel camera. If you aren't printing big, a modern 16 mp camera (or less) is fine. The current generation of Micro 43 cameras look awfully good on a 3880 on 17x22" paper, while the A7r and D810 need a big printer to show their stuff. Big printers are big commitments - anything bigger than a 3880 is in a different class from desktop printing you may have done.