Trance is well known as relaxing, harmony electronic music composed using smooth instruments.
Since various artists released trance seperated to a LOT of subgenres like:
Psy-trance (goa)
Hard Trance
Tech Trance
Progressive trance
But original trance is described as the top of this thread.
Psybient and goa are my favourite. Followed probably by ambient trance
As a quick clarification, goa and psytrance aren't the same. Goa is trance with an indian influence (particularly in harmony and melodic pattern), psytrance is goa without the indian influence.