Hi currently, i have a level 20 sniper, and a level ten assassin, i was wondering if i could get some advice on which to play - As an example in WoW, i played a Death Knight which i loved (melee with some dots) and a hunter. Both classes would be played as DPS
PVE - which class is in higher demand, and does better damage?
For the DPS role, sniper is better. Asssasins make better tanks than DPS in endgame raid settings as a general rule.
FUN - Which class is funner, and has a more complex (not too complex!) rotation
Fun is way to subjective. Rotation depends heavily on spec, so it's hard to say.
Levelling - which class is easier and funner to level?
I don't think there is all that much difference. No "class" is hard to level, although some specs are easier than others.
Snipers do have a bit of an issue in that they don't get their 2nd real companion until around L28-30. Then their healer companion on the early 30s (after that it's easy leveling). The inquisitor gets their 2nd companion a bit earlier, but it's still in the mid 20s.
They both get a tank then DPS companion as their first 2.
Storyline - Which class has a better storyline?
Generally speaking, the IA storyline is more engaging and unexpected. It is often considered the best storyline. The inquisitor is more of a standard power struggle and somewhat more predictable.
Overall though, it's very subjective which is better and is mostly personal preference.
PVP - (not that important) which class plays better in warzones?
Either work, with a lean to assasin b/c of utiliy.