Currently and somewhat unsurprisingly, Green Suns Zenith sees the most play in the most tutor-loving format, Commander
Though not all players will want to run this card, it will likely see play among more oppressive strategies that try to limit an opponents ability to play their game
Its first ability goes beyond the typical card draw effects of other Teferi planeswalkers by untapping your lands, leaving you poised for a counterspell throughout your opponent's turn
While Krav possesses characteristically Black abilities that allow its controller to sacrifice creatures for numerous forms of value, such as cards and life, Regna is characteristically White, creating Soldier tokens each turn as long as her controller is gaining life
Even if you reveal the entire library this way, putting it on the bottom in a random order doesn't count as "shuffling" the library