Change your strings regularly, depending on how often you play. If you see signs of corrosion or rust, or your guitar is losing its resonance and sounding tinny, it's time to change the strings.
Experimenting with different brands is great, but once you a find a brand and gauge you like, stick with it. Your guitar will thank you for it. Constantly changing string gauges usually involves adjustments to the neck, which can be a time-consuming pain, and wouldn't you rather be playing?