Influence of neighboring fluorine and hydroxyl on carbocation
The answer is actually quite straightforward. Fluorine is more electronegative than oxygen, thus it is less willing to share its lone pair with the carbon bearing the positive formal charge. Thus, the $\ce {-OH}$ group provides greater stabilisation. In fact, the donation of the lone pair by the $\ce {O}$ generates a familiar moiety, an epoxide. The donation by $\ce {F}$ is almost negligible since the positive formal charge on $\ce {F}$ would be highly unfavoured.