Should I use conventional mortar or self-leveling mortar for the screed?

Self-leveling mortar is much better for the base layer because it distributes itself and creates a flat surface without you having to manually smooth it out, which saves time and guarantees a more uniform result. Conventional mortar requires more skill and effort to get it leveled, especially in large areas. If the floor has lots of irregularities or uneven spots, self-leveling mortar handles that no problem, so the extra investment is worth it.