I was in Singapore for a business trip and went on the 1/2 day historical Singapore tour (2:00 - 6:00), and was SO glad to have done this! Waiman, our guide, was wonderful: a native and full of interesting and personal historical stories, very thorough and detail-oriented, and very eager to show us all he could of his city in our 4 hours. It was a great overview of different parts of the city, and would be a great thing to do early in your trip to Singapore.
I was a little nervous about doing the tour in the heat and humidity, but it really wasn't too bad! Waiman made sure to stop in shady places, had brought multiple water bottles for us all, and there was always a breeze that made the temperature bearable.
I had trouble finding the location of the bike rental and ended up calling one of the guides that was not running my tour, but they answered right away and were very helpful in assisting me to find the shop.
I would recommend this company and the Historical Tour very highly!
Thanks Waiman, for such a great view of your city.