I stayed at Roberson Quay, a small hotel with small room and stand-only shower room. But I do like this hotel because of its quiet location. Cheap too.
I also stayed at Royal Plaza on Scotts, a fine hotel with regular size room. Location wise, excellent. I paid around US$100 per it during the weekend.
I also stayed at The Oriental. The best, compared to the others. Good service but too expensive.
There is another one I like is Golden Landmark. Good size bed and room. I believe I paid around USD60 per night for it. There is a bugis MRT station close by.
If it is just me, I would stay at Roberson Quay. If I am on business, I would stay at the Oriental or Excelsior. If I am with the family, I would stay at Royal Plaza on Scotts.