Bored Topic, but now i know how harsh it is: esf or sis

My kid got an offer from sis for py1, and recently esf accepted him for k2 this fall, but they mentioned that there will be no interview priority for primaries (coming year is the final year for priority). My son's character is lack of self confidence and emotional, he avoids a task or challenge without even trying, especially on new thing or in new environment.

I believe Esf is a good school to build up his confidence. I feel very happy knowing esf accepted him. However, the feeling of fear keeps me stuck while I'm thinking of the priority system... Everyone in the kinder guarantee an interview's chance but him... Even he has interview, can he perform well within the few minutes As mentioned, he is not the type of expressive and receptive child, at least comparing with other esf kids. SIS is a train through school, should I just give up my dream school and take the safety route?