You dont have to give up any faction, but BB and SC have the most used gear for the necro. A lot of ppl start with SC and betray them for LL to get the Cloak. If you want to save time you better of with getting BB gear and go for the LL coak. Its only feet and wrist that you need to be rank 4 to buy, and the rest you can buy anyway with rare tokens or get from hm drops.
Other factions:
The Children of yag have a nice ring you can aim for.
The Tamerian Tigers have a nice neck.