Each has different advantages. I own both and both are great tools. For cutting thick wire, the Twin Force has greater leverage at the neck. For cutting at the tip, the Fantastico's have better tip leverage. When the Fantastico's open, they open with less angle between the blades, meaning the leverage difference between the tip end and the neck is less. The Twin Force open to a wider angle faster, due to the closer fulcrum.
In action, both cutters are great. The Twin Force cuts a 16 penny nail much easier than the Fantasticos, although both can do the job. Neither is ideal (Cobolt cuts right through).
Neither cutter has a large jaw capacity but that is the price you pay for leverage. In both cases, the cut piece has a tendency to jet outward - more so with Twin Force than Fantastico due to the angles. To cut large material with either it is necessary to bite, rebite, rebite again...until you are as close to the neck as you can get for the thickest portion of the cut.
The only way to get wider openings and less tendency for the cut material to run away would be longer handles - i.e. 10" diagonals or other. Both of these are compact versions and they work well.
The Fantasticos have a nonsymmetrical opening action so swapping righty to lefty for cutting is slightly more cumbersome, but they outperform the Twinforce on tip cutting. They also are bulkier than the Twinforce, so it really depends what you are after.
I ran some calcs on all of my cutters as far as mechanical advantage on tip and neck goes if you are interested in the numbers.
