To some extent it depends on what you mean by best for a DIYer. From an "easy to get factory parts" standpoint Zeagle, Hog and DiveRite are good choices and they are all good quality regs. All of them are more or less based on the Apeks design.
If you are looking for the easiest to DIY from a repair point of view, my choices changes a little.
For first stages that are very easy to service then pretty much any flow by piston first stages- Scubapro MK-2 is a great choice. It requires no special tools, is very simple to repair and all the service parts can be DIYed or are standard off the shelf parts. It is an easy first self service reg to learn on. A slightly more difficult reg to service and to get parts for is the ScuabPro MK-5. The parts issue has almost been solved by the DIYers here. Oring size charts are already posted and the HP seats can be home made or from what I understand Trident is now making a replacement. You do need a couple of special tools but they are easy to DIY or can be had at a fairly low cost. All in all, most likely the best overall choice for a DIYer first stage is one of the later MK-5s.
If you want a balanced second stage then I would go with the Zeagles, Hogs or Diverites again due to the easy of factory parts kits. If however you don't reguire a balanced second stages then there are lots of choices. Pretty much any of the older metal second stages (from the 70s and 80s- don't go back to the 50 and 60 and avoid Healthways and Sportways) and most of the plastic non balanced ones use common parts or parts than can be DIYed. The best of them is the Scubapro 109. It's an adjustable metal second stage that performs very well. Most of the internal parts are easy to get/DIY with the exception of the diaphram and exhause valves, both of which do not require changing often and can be had if you look around some....or have it serviced once at a shop just to get the parts.
If you are just starting out, then the first things you need to buy are a couple of books. They will help you understand the internal working of regulators and give you some ideas on what special tools you will need. The 2 books are "Regulator Savvy"
Scuba Tools and "Maintenance and Repair of Scuba Regulators"
Airspeed Press Homepage - Books For Serious Divers . I suggest you get and read both of them. Each has a slightly different slant on service and repair and between the 2 you get a solid foundation to work from.