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There are MANY threads for all of the hotel loyalty programs under Miles & Points/Hotel Programs. Starting to read the main ones may assist you in making your decision.
If you are going to be somewhere for a month and don't mind switching back and forth between hotels it would be a great opportunity for you to get a good jumpstart on the programs you want for their top tier. For example, Starwood requires 25 STAYS for Platinum (their top tier) and Hyatt requires 25 STAYS for Diamond. If you have 30 nights for the month in SIN you can easily have 15 stays for each program if you go back and forth between two properties during your stay. Just a suggestion.
I would recommend you visit the Hotel forums to help make your decision.