Flying Singapore Airlines - KrisFlyer or United?

Hi,

I am flying from London-SG-Jakarta and back to London (via SG) in J (Full Fare Business) class.... I am not a KrisFlyer member yet but I am a United Silver.... Would it be worth adding these miles to KrisFlyer or MileagePlus?

I contacted Singapore Airlines and they told me I'd get around 19k miles if I signed up for KrisFlyer but neither SQ nor United were able to tell me how many points would I get on MileagePlus for this trip... Any idea what this equates to in MileagePlus?

I want to make sure I add these miles to the correct program so I don't lose out!

Thanks guys! :))