Parcel 2 go are the best in my opinion. This is because if you have a contract with a courier, you can send parcels for much cheaper, but to have a contract you need to send parcels really quite often. However, if you don't have a contract, then the price get's much much more expensive. And so with parcel 2 go, they have the contract with the courier, so they get to post the parcels for cheap, and you pay parcel 2 go to get this. So basically, it's much cheaper for you as instead of paying the massive non-contract price, you pay a price somewhere in the middle, and parcel 2 go posts it via the courier.
Get what I mean?