We used Express Translation and they were great. They took care of absolutely everything to do with the Amphur. We took them all our documents so they could copy and pre send to the Amphur to prepare everything. Then, we just showed up to their office and they had a taxi for us to the Amphur, which was about an hour from downtown.
At the Amphur, the translator took care of everything and we just waited and signed the papers when they were given to us.
I had already gotten my affidavit to marry from my embassy and had it translated and certified at the Thai Ministry by another translation company, but that first place didn't have any contacts to get the Amphur registration done.