I usually head from Sembawang to Bedok using
MRT to Woodlands > 168 or
962 > 168 if I have time.
Going via 858 from Yishun include multiple transfers, so time
will be wasted on waiting alone. The freq of 858 isn't exactly
fantastic. Plus loading is mostly on the high scale.
I don't exactly recommend going via Toa Payoh as it will
definitely take a longer time compared to taking 168 direct from
Woodlands.
As for the other suggestions here, they are complete
nonsense.
i dun think my suggestion was nonsense.