Does your budget enough to purchase 2 specimens? They are all excellent material and if handle appropriately will improve exponentially with time. I say purchase the deciduous and a juniper.
Sabina’s can be a bit of a handful if not looked after correctly. May not be the best choice for a rank beginner. So maybe the Prunus would be a better choice.
@Nicknjh23 I second that, deciduous is usually a little more forgiving in terms of the care they need. Except for a lack of water, junipers like to be drier but even then they still need water.
I would buy a handful of cheap trees, rather than one nice one. You will learn much more, and risk less. My two cents. Full disclosure: I’m cheap and have no access to pre-bonsai. I may just be jealous…