I have used both service (although SNS I have used very less) and till now PPOBOX was definately better than SNS in almost all respects.. first of all registration was free (but that doesn't matter much to most ppl), shipping was quicker between 3-7 working days from the day it reaches their NY hub and no hasstles like the requirement of order invoice/ transaction details and seller/shipper's name/address.
However now I am expecting that their service standard and consumer experiences are going to get hurt with this regulatory audit. I talked to their manager Sanjay Ghosal on friday and these guys now seem to be very cautious after the audit and even willing to loose business if the custom guidelines are not met to the word.
The biggest thing that bugged me about the SNS was the custom value declaration and duty calculation on that was completely in their hands.. even if u buy a used phone for 200$ whose retail value is 400$ , they used to mark value is 300-350, but in PPOBOX whatever value u declare , fee was caluclated on that. but now , after the audit, even if I am providing them paypal invoices and reasons on why the item is sold significantly cheaper than its price, they are not ready to consider that value for custom fee calc and blatantly say that if it get stuck in custom , then its our responsibility to talk to them and get it cleared.
So, till now PPOBOX experience was really better than SNS and from now I am not so sure.