In HK's urban standard, HP is in the middle of nowhere IMHO. You have to take a taxi or shuttle to other places.
LP on the other hand may be a bit too urban for visitors, since it's in the middle of one of the biggest shopping district in HK, sometime it's hard to walk through nearby streets.
Have you considered the other Langham in TST? It's just 5 mins walk from TST subway or the Star Ferry pier yet not overly congested.
This is the real difference between the 2 hotels - HP is more leisurely: you are next to the water, restaurants and shops are more spread out, there are "fewer" people around. While LP is in Mongkok - a shopping haven for most people - but maybe a bit overwhelming for foreign visitors.
Langham hotel in TST is a good choice with a little bit of both hotels.
We have stayed at the Langham Place every year since it opened (yearly family visit), and now my husband stays there monthly for his business trips. We have always enjoyed the good service and modern, clean rooms.
Have you made your choice?