Rate constants can be derived from the dataset published on the website [http://udfa.net].  Rate constants have the form:
k(T) = alpha*(T/300)*exp(-gamma/T)cms
The following table has the rate constants calculated for a typical temperature in a dense cloud T=10 K.
Formation rates r can be obtained using the rate constants k(T) and the abundances of the reactants species C and D:
r=k(T)[C][D]
where [Y] represents the abundance of the specie Y.  In this approach, abundances were taken from The UMIST database for astrochemistry 2006, and the values are relatives to the H density.  Following table shows the ratio r/r in order to get a view of the most important reactions.
The results suggest that (1a) reaction is the most prominent reaction in dense clouds.  It is in concordance with Harju et al. 2000.
Next table shows the results by doing the same procedure for destruction reaction:
Results shows that, 1A reaction is the main sink for HO in dense clouds.