I might go so far as to change/empty the maintenance tank regardless of what procedure you're using - ink sloshing around is NEVER a good thing...I was present when an iPF 8300 was lost to an ink spill - Canons are far more vulnerable to ink spillage while moving than Epsons, due to their subtank system, but loose ink is a concern for any big printer, and the maintenance tank is a prime source of loose ink! Epson also says to lock the printhead in place by reinstalling the piece of packaging that held it during initial shipment. I lock printheads on ALL printers larger than 8.5x11" if I'm doing more than rolling them around the room - I keep the appropriate piece of packaging in the pocket Epson (or Canon) provides to store the manual! HP suggests taping doors and flaps shut, and I'd think that would be excellent advice on any printer (I've even taped doors on 8.5x11" printers).
Epson says to leave the cartridges in (I assume to maintain pressure in the pressurized ink system - the lines would actually be more of a concern if they weren't capped off by cartridges). They used to advise using EMPTY cartridges, which seems like it might a good idea if you have some available. Empties (or near-empties) should keep the pressure system charged, but limit the amount of ink in play if something jostles (they're also a good deal lighter than, say, full 700 ml carts). I've moved a bunch of 17" Epsons without issue, and just installed a new 7900, but it'll be a year or more until I have to move that thing with ink in it.
Canon advises removing the cartridges and draining various bits of the printer, depending on how far you have to move it, and how much you have to tip it (the "Level 3 move", which drains all ink, loses so much ink that it can cost most of the value of the printer). I'd be extremely careful with any iPF that you can get it into and out of where it's going LEVEL (or that it's going somewhere where it'll never have to move). I've manhandled 5000s and 5100s (17") about quite a bit with no issues, moved a 6100 (24" once with relatively minor tilting, and it was fine (didn't drain it, but the 6100 didn't have the subtanks that were added to the 24" line in the 6400, but have always been present in the 44" models), and was at an unsuccessful 8300 (44") move (despite a Level 2 drain and removed cartridges).
I've never had an HP, but their manual suggests that HPs are the most forgiving of all to move. No exhortations at all about keeping it level or even locking the printhead. They say you shouldn't remove cartridges or heads (and I don't know if the empty cartridge trick has value here).
