Well... In my experience, and from what I've heard from others, the ACA route along the east coast often takes you through rural areas and areas of nothingness with gaps in services. The ECG, on the other hand, tends to run you through more urban areas using off-road and bike lane routes where possible.
If you are looking to do the trip in the summer months the coast is very busy... and expensive. I did some on-line checking of campgrounds and a KOA near Myrtle Beach was, as I recall, about $48/night for a tent site! If you hang near the coast try to make reservations as rooms and camp sites seem to be full, especially Thursday through Sunday. Compare that to a Motel 6 along I-95 for $35 with the AAA (or maybe it was AARP) discount. In Savannah if it were not for a road angel who let us use his guest house we would have been in trouble. This as every hotel/motel I checked was full and I didn't find any campgrounds.
My son and I found US 301 through NC to be a great route last week. The only area traffic was at all congested was near Wilson. Most of the way there were fine shoulders, no buzz bars and little traffic. Due to it's proximity to I-95 short detours from US 301 will take you to food and lodging with no problem if you happen to be in a lightly populated area along US 301. I noticed that access to services is better now than what I experienced in 1986 as I-95 has matured since then.
I've also noticed that between 1986 and now that there are a lot fewer campgrounds and many of those that exist don't have specific tent sites. Stealth camping along the coast would seem to be problematic due to the density of development... but I guess it depends upon how much nerve you have!
We have the ACA maps, the ECG maps via the web, and AAA state maps. The AAA maps seem to have had the most use as the rural vs urban issues, access to services, route interruptions, and the congestion issues we've faced drove us from the ACA and ECG routes. We used part of one ACA map thus far... and a section of the ECG route but have mostly used our own course north.
I think that the season you take your trip will influence your experience. In 1986 I started in FL in the winter and rode north into the spring. It was cold at times but the tourist areas were often empty and prices were cheap! On this trip a dive motel in a crap town about 50 miles from Myrtle Beach was $102 and the few chains in the town were a lot more expensive than that... no campgrounds were found.
In my opinion, the AAA state maps are about all you really need on the east coast if you learn to read them. The different types of road codes and the degree of meandering give you a very good idea of what you will encounter. Combined with a smartphone it's pretty easy to figure out what kinds of services will be available along the way too. But that's me... how comfortable you are with bushwhacking your own route should be a deciding factor here.
Also, along different segments of the coast one route may have advantages over the other. If money isn't a huge problem maybe study the ECG, ACA, and AAA maps and the fee version of Map My Ride and get a feel for the roads. With the Map My Ride fly over feature you can plot a route and then fly over it to see what the road is like... bike lanes, buzz bars, etc. can be seen on the fly overs.