Which value to use when Calibrating Altimeter Manually?

NOT the GPS altimeter. GPS is terrible for height measurements without "extra help". 

The location based might be best - but best way is to figure out your actual height when you calibrate the watch. Airport Altimeters are not updated continuously.  

So if you can find a height map of where you live - then if you are not on the ground floor add about 3m per floor > ground.  That will then be your true altitude (roughly) - then wait for an update from the airport showing the hPa. (Lookup "METAR" data from Brunei airport - it will show how "old" a reading is. (Ground floor = 10m - 1st = 13 - 2nd = 16 etc)

If there is very little wind - you can usually just use the Airports latest reading without waiting (Isobars are far between) - but if it is windy - wait for the hPa update from the airport (isobars are close together when it is windy - so hPa change usually happen quicker)

It is slightly more complicated than that - but I think that would give you good results.  You can do better but that require you to view the maps with Isobars and interpolate between them and your current location. Not so easy and not perfect either.