I once had a less-than-stellar experience with
Greek Box (order was seriously delayed -- letters ordered in November and intended to be a Christmas present arrived in February), but because they had a very cute ladies' cut pullover hoodie, I gave them another try. This time, the letters arrived within two weeks of ordering. Go figure...
Delivery speed aside, Greek Box's letters are very high quality and are stitched on with a thick, smooth-looking finish. I would order from them again.