Rock Auto are okay but I have found the service from DHL/Parcel Force pretty poor.
It seems to take a long time for anything to happen and you have to go through a succession of tracking numbers and reference numbers to keep an eye on things.
My only real grumble with Rock Auto was when I ordered a load of bits for my MOT and they sent it in six different parcels, each of which raised customs charges and VAT (fair enough) and Parcel Force admin fees (Grrr!) which add up fairly quickly.
I've learned that, if it's possible, go for the FedEx option every time. It is so much faster and the VAT is prepaid. I ordered some bits on Tuesday this week and FedEx delivered them on Thursday morning.