I won't claim to be an expert of any kind. Do your research specific to the context in which you intend to use it.

The last time I made any pepper spray purchases the consensus of people I polled preferred stream. The people whose opinions I solicited were primarily law enforcement and/or combatives practitioners.

IIRC the primary strike against foam or gel was usually that in a close hand to hand confrontation it was too common for the person on the receiving end of the spray to simply wipe it off and then apply it to the person that had deployed the spray.