Demo is a well-rounded class. Strong, pretty straithforward nuker. Has the best AoE burst damage in the game; a real horror show.
Necro is a bit weird - has some really useless abilities, but also some really great ones. More difficult to learn, but more versatile in the end.
As a raidleader, I prefer demos, as they can serve as a secondary healer (surprising, but true - the get an automatic group heal in the end). But both are highly sought after in raids nowadays.
If you're looking for somebody to make a decision for you... try Demo first. There's nothing to stop you from switching to Necro later or play both. And Demo makes it easier to concentrate on the game mechanics first without worrying about 20+ weird spells.
In my view, it's like choosing between a swiss army knife and a no-nonsense switchblade when trying to learn how to cut an apple: The swiss army knife may allow you to do really fancy stuff to that apple and repair your bike at the same time, but the switchblade will do the job just fine without the danger of breaking something.
Make Hyboria raid again!
Khaletoheps AoC-Youtube-Channel:
http://www.youtube.com/user/Khaletohep
Guides zu Klassen & allen HM-Solo-Inis:
http://www.nachtwind-gilde.com/guide...-age-of-conan/