The capacitor bank on HT side will anyhow correct the PF,
the line losses will not be reduced. hence by putting the
capacitors on LT side, that too nearer to the load, the
losses and PF can be much better improved. The capacitors on
HT side is just to minimize the line losses, even though it
improves PF putting capacitors on LT side is always
recommended that too nearer to load, so as to get efficient
usage of electricity.
 Please not that this answer is only for inductive load
consideration as linelosses and transformers and most of the
loads conneted to the line is inductive.