It's personal preference mostly. Although, if i am correct, not all guardians begin with the ability to use [i][u]all[/u][/i] of the three elements. Titans can only access solar light (Sunbreaker) if they visit the Forge on Mercury first and Warlocks can only use arc light (Stormcaller) if they absorb the power of an Arc Storm first (or something like that. I don't remember exactly). Hunters might be different however. If i am correct they don't need to go to an outside source to wield void light (Nightstalker), however it is extremely difficult and dangerous for Hunters to try and master void light.