The SSRs you have are all pretty good, but by themselves is not nearly enough to rival a leveled up fire team (I assume you have some good SSRs on that team), so I would decide based on events.
Thunder would be the standard complement to cover fire's weakness to water, but the next water event is next week, and then not another one for a few months, so I would work on the wind grid, since you will need it for tower.