I would go with the A/C because it will help both ways. Unless your running CO2 then you need the ambient temps to be higher.

Ours stay at 72 degrees, water stays at 72. I looked at chillers but no amount of venting will help this heat 95 to 100 all summer and then lights on top of that. Some chillers only drop the ambient temps by 10 degrees. Still doesn't help me in summer.