I have Better MAgic installed, but after looking at Mighty Magic that looks great, too. I also have Forgotten Magic installed for some extra spells.

What are your opinions on Better Magic vs Mighty Magic?

Also, if I wanted to use Mighty Magic instead with a new character, could I just deselect and uninstall the Bette rMAgic mod in NMM, install Mighty MAgic and use it? Will Mighty Magic work with Forgotten Magic?

I don't personally use either one, but I've looked at both extensively. IMO, Better Magic is much more thoughtout than Mighty Magick for Destruction, but offers basically nothing outside of Destruction, while Mighty Magick tries to be comprehensive (but both feel like destruction was the only school either of the creators really was interested in).