Sage is better in 1v1 and more fun in mass if played correctly (it's the easier side to play)
Demon is more useful in mass because of purge chances, but it is actually harder to properly play. It has a shorter stun, and often runs into chi issues in 1v1. It is also more expensive to be well geared as a demon. If you have proper CC classes with you in mass to control your targets, a demon aps archer will eat every arcane and LA easily. Demon archers aps are also useful if you don't have a wf available for purging hard targets.
Sages traditionally build to either be channeling ea's or dex ea's. I have a set for both builds, and I can't honestly decide which one I like more. Chan/dex stats are a whole lot easier to get your hands on, making sage a cheaper alternative while still being effective. This is definitely the easier option unless you're like me and you have the ec to make 2 of everything.
In terms of gear choice as a sage, since you're new, build for chan. It is a lot easier to play. Do not learn the new primal skills btw. And do not wear dragon ever. ok bye