I would have to say it depends: do they face eachother in the matrix, where Smith rules? or in the real world, where Smith is forced to inhabit a human meat puppet in order to survive?
In the Matrix, Smith and all his clones and viruses and skills at manipulating code would have T-101 deleted in no time..
in the real world, T-101 would terminate any human meat puppet Smith would inhabit, unless the meat puppet was Sarah or John Connor, or Katherine Brewster, or Kyle Reese, in which case, T-101 might still hand them their own entrails, if the meat puppets were not allowed to 'be themselves' to out-think the T-101, based upon all their stored knowledge of the Terminator... if Smith, as a meat puppet John Connor, had access to all John's thoughts and ideas, then Smith might also be able to take T-101, especially if T-101 was the reprogrammed model, who was set to befriend John, and was caught unaware of John's own 'new program,' Smith...
it all depends on a lot of variables, really... so you need to be more specific with the question, I think.