The answer here is really easy “neither”!
The first real fact about tornados is that they don’t follow the contours of the ground, so for deep depressions or ditches they pass over them and not into them. The terminal velocity of a tornado could conceivably suck a person out if all the ceiling was gone and they are standing up in the middle. Honestly, I can’t say I have ever heard of a basement being totally sucked out and anyone being pulled from it. The reality is that people are told to move to a corner of the basement where the walls can protect you. Even FEMA suggests that you move to a corner and place a mattress or something like it on top of you. When it comes to things easily falling on top of you, consider the floor joists above you. The majority of houses that are hit by a tornado tend to have most of it collapse on itself. For other houses that are nearly blown away, the basement tends to have most of its floor joists intact. It may have gaps, but it is very rare for all of it to be blown away. That is why in areas where an entire town is destroyed by a tornado, basement homes tend to reduce the number of lives lost.
Referring to an article called “The Straight Dope” by Cecil Adams, written July 29, 2011, he answers this question followed up with real stats.
It says, and I quote: “An analysis of the Oklahoma twister outbreak of May 1999, which featured an EF5 (i.e., scale-topping monster) tornado, found that out of forty deaths, 133 severe injuries, and 265 minor injuries, the total harm inflicted on people holed up in basements amounted to just one minor injury. In the Joplin, Missouri area — where the death toll stands at a staggering 155 following the tornado of May 22 — 82 percent of homes had no basements.” I could not have said it better myself.