Hello! Hope I'm not too late.
Westin - food is great, atmosphere is great, service is great. Cost is so-so. Comes with the presidential suite, which is HUGE, with its own jacuzzi, sauna all inside. The suite is so big that if you talk normally at one end, another person at the other end will not be able to hear you.
Shangrila - food is great (of course), atmosphere is great (of course), service is great (of course). Cost is...er....well, you know lah. Comes with a suite which somehow looks disappointingly like a nicely decorated chalet to me. Not half as nice as Westin's. I think Shangrila has a package which includes a night in the hotel on the first anniversary.
M Hotel - food is great, atmosphere is not 5-star but acceptable, service was good too. Affordable. Comes with room which is very small but modern.
Hyatt Hotel - food is great but not enough, atmosphere is great, service was great. Cost is high, I think. Never got to see the room - this time, the bride didn't want to be close to me

.
Mandarin Hotel - food is great, atmosphere is great, service is great. Cost must be high lah. Never got to see the room - this time, I didn't want to be close to the wife (too hot tempered...not my type

).
Many people don't realise this, but whats very important is a wedding butler. He/she takes away 50% of the stress because he is like a backstage prompter, personal assistant, etc. He will give you advice first (normal formalities), then prompt you in time what to do (eg. change dress, etc)....and will attend to any eventualities that night. And unforseen things WILL occur.
Disclaimer 1: I'm usually a hungry person and any food tastes great to me.
Disclaimer 2: Its hard to estimate the service during dinner because most of the waiters/waitresses are part-time workers, so it really depends on luck.