I have been using MagicISO and PowerISO for a long time, and I sincerely think that PowerISO is more practical than MagicISO.
MagicISO is a huge time Hog. Ever tried to mount an *.uif? It starts a lengthy uif verification every time you mount your file, which is totally unnecessary. PowerISO does not trouble you with *.daa verification, it just mounts your image.
Every time you make a slight change to your image file, MagicISO "recompiles" the whole thing, hence losing a lot of time. PowerISO on the other hand, spots the change and save only the change that occurs, in a snap. This gives PowerISO one edge over MagicISO.
Another thing, MagicISO does not have an in-built mount software. You have to download an addon called MagicDisc and install it.
I have seen portable PowerISO, and it was really handy to carry it around in my pendrive and use it without installation. But this isn't a great deal, because portable PowerISO cannot mount images; it can only make images from folders and drives, just like a portable MagicISO (without magicdisc) could.
However, if you engage into complex image functions, like multiboot (which very few people out there might use), then you might consider ultraISO or magicISO. Notw however, PowerISO can make simple bootable images, like a linux bootable CD/DVD.
I hope my review helped you make a good choice.