I've been going to Singapore once a month for a week at a time for the last 10 months and I have been using Starhub's prepaid microsim with my iphone 4s. The data performance in woeful to say the lease, I find myself waiting and waiting for a simple page to load from the most reputable sites, and this happens more often than not. My traveling partner using an android has experienced identical issues at the same time. Does Starhub give priority to postpaid customers for data access and if so what are the alternatives? I usually sign up for 1gb for 7 days.
Singapore's mobile internet speeds are not exactly the fastest compared to its counterparts in East Asia - this Reuters article SingTel admits its wireless is slow, vows changes provides some insight into the issue.
The article does mention Singtel specifically but based on what I hear from friends, the speeds are barely sufficient for all 3 telcos. I'm using Singtel myself (postpaid, occasionally using a prepaid card for testing) and the experience varies from "OK" to "horrible" depending on location.
I'm afraid there aren't many alternatives without giving up the convenience of always-on data access.
All telco providers in Singapore are currently having this issue, especially in crowded area ( especially Orchard ) , during lunch time or after office hour. So, there is no alternative for your problem.
You can also refer to this article.
It caused by a high adoption of mobile internet in Singapore. Singaporeans are the global leaders for the longest time spent on Facebook. Read the article here.