I haven't flown the OZ 767 ICN-SIN to comment (only the A330), but as far as the SQ603 is concerned, I frequent on this route and in some cases SQ603 it arrives really really early.
On the 603, because of the past midnight departure time and then the super early breakfast service (mind you, it is a 'sleeper' service), I hardly get any sleep at all on this one and I normally end up skipping all meals and having breakfast at the Silverkris lounge.
So given the two choices, I might probably try the OZ753 if it was the choice between that and SQ603.
But, I've never taken OZ753 because that schedule basically overlaps with SQ16. If SQ16 is an option for you, I know what I'd choose :P