Welcome savuok!
I'm not certain which of those two models would suit your needs best, but I can tell you either of them has a wide variety of tonal possibility. There are many players here from virtually every kind of music, who might better advise you.
Some differences between these models:
Essence has low pass filter for a tone circuit, where Epic (also Orion & Excel) has a Bass & Treble boost and cut rotary control. Opinions and tastes vary, but Alembic is known the world over for these filters. It's a totally different way of shaping your sound. I cannot describe it.
Here are links to information on the controls of each model:
http://club.alembic.com/Images/16271/16345.html?1307055464 http://club.alembic.com/Images/16271/18781.html?1307501227 Essence also is a standard neck-through design, where Epic & Orion are set-neck. This feature has much to do with sustain/decay of notes.
Again, welcome to our little corner of the internet. There is a wealth of information here in these pages, and a large group of Alembic-experienced players are always happy to help. Quite often the General Manager (we sometimes refer to her as the Head Elf) Mica Wickersham Thomas drops in to opine or respond to questions.
Happy Hunting for your first Alembic! Keep checking the Swap Shop here for a good deal on a used bass.