hi erushi,
i guess you have to consider a number of things like the food menu, ballroom, service of the hotel staff attending to you, location of the hotel and also, the availability of your preferred date.
for me, i go for gpph, even though it's more expensive. cos i preferred the food menu there and it's ballroom doesn't have pillars (think empress ballroom of carlton has 2 right?). as for location, both carlton and gpph are located near the mrt station, so accesibility to the hotels shouldn't be a problem. i din have a chance to meet up with carlton staff, so not too sure of their service.