Of the three, Trip is my favourite character, however for the purpose of this poll I went with T'Pol. She has more experience than the other two combined, generally more level-headed and understands how things work in the galaxy at that time.
Commander Austin Harris, First Officer, Deep Space Nine (by FltCpt. Bossco)
8.01 - Darkest Before Dawn
(Chapter 8 added, 12/09/2015)