I would choose 真光 since they have their own primary school - & a decent primary school too.
If the kid is bright, she can still apply to SPCC, DGS etc.
Sure 聖保羅堂 考小一OK, but there is nonethless uncertainty.
One bird in hand is worth more than two in the bush - I would rather be sure to have a decent primary school as back-up right from the start!