spell slot 1 refreshes some milliseconds faster than the other spell slots. So it's personal preference really. I usually keep a life saver spell in slot 1. Like Stun.
Shrunken Goblin Skull Earring works perfectly to reset the global cooldown. There are some other options. Pretty much anything instant, just keep in mind if it's all zones or outdoors/indoors only. Jboots are an example of outdoors.
https://wiki.project1999.com/Clickies
https://wiki.project1999.com/Balers_...#GCD_Resetters