We have a bunch of the serrated cardboard knives and they work really well if you value precision over speed. If you are constructing things out of cardboard, these are great. If you just need to cut down some boxes so they fit in the recycle bin, one of the other options is going to be faster.
As for the electric cutter/rotary things, I’ve never used one, but the Project Farm guy really liked the one from Skil. It’s even show up in other videos when he was cutting paper or cardboard strips.
