When considering bond angles of molecules of main group ($\ce{\angle A-X-B}$) there are several different factors to consider:
- The row of the the central atom $\ce{X}$ determines the energy difference between the valence s and p orbital, which determines the extent of mixing (or hybridisation if you wish)
- The sizes of A and B, because steric repulsion, A and B would want to stay away from each other the bigger they get.
- Electronegativities of the A and B. More electronegative atoms would prefer to have a bond with higher p-character. (This is explained in VSEPR model with the bond pair being drawn away from the central atom)
- Other forces betwen A and B
The bond angles of the molecules mentioned in question are:
$$\begin{array} {c|c}\hline & \text{bond angle} \\ \hline \ce{OF2} & 103.2^\circ \\ \hline \ce{SF2} & 98^\circ \\ \hline \ce{HOF} & 97.2^\circ \\ \hline \end{array}$$
The difference between $\ce{OF2}$ and $\ce{SF2}$ would be usually explained with the fact that oxygen is in 2nd period so, the energy difference between $\mathrm{2s}$ and $\mathrm{2p}$ is low which means it is $\mathrm{sp^3}$ hybridised. (Or at least close to $\mathrm{sp^3}$). Whereas sulfur is in the 3rd period so, the energy difference between $\text{3s}$ and $\text{3p}$ is high which means it is almost unhybridised and the bonds are formed by almost pure $\text{3p}$ (which is why the angle is closer to $90^\circ$).
The bond angle of $\ce{HOF}$ is however, unusally small. This is difficult to explain and is usually attributed to the electrostatic attraction between $\delta+\;$ of H and $\delta-\;$ of F, which pulls the H and F close together.
From Chemistry of the Elements [1],
Spectroscopic data establish a nonlinear structure with $\ce{H-O}$ $\pu{96.4 pm}$, $\ce{O-F}$ $\pu{144.2 pm}$, and bond angle $\ce{H-O-F}$ $97.2^\circ$: this is the smallest known bond angle at an unrestricted O atom (cf. $\ce{H-O-H}$ $104.7^\circ$, $\ce{F-O-F}$ $103.2^\circ$). It has been suggested that this arises in part from eletrostatic attraction of the 2 terminal atoms, since NMR data lead to a charge of $\sim+0.5e$ on H and $\sim-0.5e$ on F.
So, the unusually small bond angle is likely from the electrostatic attraction. This type of effect is not just limited to $\ce{HOF}$, it is also found it other molecules. For instance, in hydrogen peroxide $\ce{H-O-O-H}$, the $\ce{H-O-O}$ angle is $94.8^\circ$ which is quite lower than the ideal tetrahedral angle, and has been attributed the electrostatic attraction between $\ce{O}$ and $\ce{H}$.[2]
As an aside, it should be noted that the above values of bond angles were measured in the gas phase. In solid phase, $\ce{HOF}$ has a slightly higher bond angle, at $101^\circ$.
References-
- N. N. Greenwood, A Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, 1998
- E. Wiberg, A. F. Holleman, N. Wiberg, Inorganic Chemistry, Academic Press, 2001