For Citibank Dividend card, at a rate of 0.5% rebate, u'll need to spend $10000 in order to get the $50 cheque. If u do not chalk up this amount by the anniversary date, whatever Dividend$ u've accumulated will be forfeited. Of cos, if u're driving and pump a lot of petrol, u'll be able to hit 50 Dividend$ much sooner. So unless u're driving or spend a lot on shopping/dinning, Dividend card is of little use.
Although the rebate percentage is lower (0.3%), POSB Everyday card is more "friendly" because u can redeem any amount of Daily$ anytime u want in the form of discount to ur SP Services and Starhub bills.
I think the best card around now UOB-Singtel card. As long as u have a Singtel account (residential or mobile or broadband), u can apply for this card (3-year subscription fee waiver). The rebate percentage is at least 0.5% and comes in the form of Smart$, and can (only) be used to offet ur Singtel bill or convert to Krisflyer Miles. Other benefits include a sign-up bonus of 50 Smart$ and free caller-ID if u're using Singtel mobile line.
A combination of POSB Everyday (for grocery shopping at Carrefour and paying SP Services and Starhub bills) and UOB-Singtel (for general shopping and Singtel bills) will be good. =)