I'll say an ABer. An SSer takes a long time for you to earn neopoints while an ABer just needs to buy for you one expensive item for you to earn around 500k. Definitely go for an ABer if you can.
Depends on where you restock and how long you ab there. A SSer can earn you alot of np but your list has to be flawless, no wrong times, not too high score and make sure there isn't a lot of people using your list.
Also with the SSer, you risk being caught out if they change the review scores and such. Whereas with an ABer, you can minimise your risk of being frozen by adjusting your settings, with an SSer you just have to hope TNT don't change anything.
I say ABer, for all the reasons already listed above, and because of one other simple fact - there aren't any working SSers right now; most of them currently send your score but don't get you the NPs.