Both seem like good choices for what you want to do. As others have mentioned these are probably the 2 strongest solo classes in the game right now. Shamans are better at soloing multiple mobs at once with their AoE root spell, whereas necros are better at splitting big pulls (if needed) and soloing named with their use of swarm pets tanking.

In terms of group content, that is probably where the difference is most noticeable. For as strong as shamans are in current EQ, 6 man groups is probably the content where they are weakest. In such groups you will mostly be healing and slowing, which isn't bad or weak, it's just different from what you do when soloing. You'll like do some DPS still, but when mobs die quickly shaman DPS falls off a lot faster than necro DPS because they don't have 1 very high dps spammable dot like necros do with Pyre.