I don't mean disrespect here, but your question is similar to asking, "I'm trying to dig a hole, and it seems like spades and 50-ton CAT excavators are common. Which one is better?" The answer, clearly, is that they are different tools for different jobs. The catch is that you have to know what the job is.
Either motor can be used to drive an arm; it's just a matter of how quickly. As Ether pointed out, the FP motors are approximately ten times more powerful than the Denso motors. At the risk of tooting my own horn, please take a look at this:
A FIRST Encounter with Physics. I wrote it specifically to answer these kinds of questions.