Honestly i have more faith in Sanders being able to answers debates and pressing questions, because he believe what he say, he fought all his life as a politicians for the things he's proposing, he's not reading from a note of "hip" things to say.
On the other hand i fear Hillary could easily show not as much firmness in her belief, if she actually has any at all since all she say seems to be extremely fake and directed. Sanders is like Trump in that sense, he's anti-estabilishment, and he fight for more personal reasons, so his words and reasoning carry more weight.
Trump would probably kill Shillary with some pressing on her donors, wall street politics and who know what other skeleton. I doubt Sanders have the kind of skeletons that could ruin his run. On the other hand, Sanders is extremely old and has the label of socialist, which in the US , as i understand, is seen as something bad.
One thing is certain. This presidential run is all about the anti-estabilishment vs the estabilishment. This shit happened like 30 years ago in Italy, and Silvio came in power for 20 years as the self-made man who was not corruptable by others cause he's rich as fuck and he represent only his self-made interests. For all the shit he said, he did remarkably little outside of the typical things rich dudes do: lower taxes on rich people, depenalize fiscal theft for rich people, and then basically nothing relevant outside of that because of fear of losing popularity, continuing a tradition of mediocrity and compromise for italian politicians.