The recommendations for Witney certainty don't fit with my impressions. Both Tactical2017 and the guardian equivalent advocate voting Labour, with the guardian adding that:
But don't get your hopes up. The combined vote of Labour, Lib Dem and the Greens would not have been enough in 2015 to beat the Conservatives.
However this does not account for the Witney 2016 By election and the moderate inclination towards Bremain in the EU referendum (537% remain). Betting odds also suggest LibDems are far stronger than Labour in Witney.
*EDIT: I wrote too soon... I just double checked and Tactical2017 have updated their page since I last checked to advocate for a Lib Dem vote.