I think you are comparing apples to oranges here. The Langham Place hotel in Mongkok is a very nice hotel but it's not the same class as the FS. The Langham Place have nice suites (make sure you get the Residential Suite and not the Langham Suite) and nice fixtures and furnishings and, in my opinion, much nicer than the Conrad, Sheraton, etc. But the FS (I have only stayed there once) have higher quality rooms and a totally different atmoshere.

The locations are also very different. The FS is at the International Finance Centre in Central on Hong Kong Island. It is in the business district with very high end shopping and restaurants. The Langham Place is attached to the Langham Place Mall and located in Mongkok. The mall is geared to the younger crowd and Mongkok is very busy and crowded. I personally prefer Mongkok because I like to walk around all the shops and restaurants there and to me, it is the real Hong Kong. However, if it is your first visit to Hong Kong, it may take a little getting used to. On weekends and most evenings, it is wall to wall people and if you are not the "adventurous" type, you will have a problem. Getting around Hong Kong is very easy for both locations as taxis are plentiful and the MTR is one of the best subway in the world.

The "Suite Deal" at the Langham Place used to be one of the best deals in town when it started a couple of years back as the rate was HK$1,999.00 but now at $3,000+, it's not a bargain any more. If you are looking for the nicer hotel, definitely the FS. If you want a very nice hotel in the middle of one of the busiest area of the city, then it's the Langham Place. Have fun and enjoy the city!