Good for you that you are taking the plunge. I came back a couple of months ago from pretty much the same trip that you are planning. I drove a new Yam XT660R and was fortunate enough to meet up with some good travelmates along the way. Before this trip I had only done tar road and some minor gravel roads. Close to none off-road experience.
The route I took was Morocco/West Sahara, Mauritania, Mali, Burkina Faso, Niger, Nigeria, Cameroon, Gabon, Congo (Brazzaville), had to airlift over Angola since we couldn't get a visa through Cabinda at the time, Namibia, Botswana, South Africa.
Your route will pretty much be dictated by where you can get visas (usually capitals). And if you plan on staying mostly on the main roads, then there's pretty much only one route you can go. Based on personal experience, I do recommend sorting your Angola visa before leaving. But do a search here on the HUBB. These things change almost daily.
If traversing the continent is your goal (as it was for me) then the east coast may be easier. But at the time when I planned my trip, there seemed to be so much trouble and paperwork involved in getting to Egypt and then into Sudan, that the west coast seemed easier in comparison. Even if it meant more countries, and thus more visas. Since I haven't traveled the east coast, I'll never know for sure if my assesment was correct. Either route will grant you a lifetime of memories, and cant honestly recommend either over the other.
Let me just add, that this was my first long trip on a motorbike. I had only gotten my drivers license for motorbike, 4 years previous to this. Experience is something you'll get along the way. Just know your limitations and take it slow. I can't remember who said this "He who travels slow, travels safe. He who travels safe, travels far". I lived by those words during my trip, sometimes to the frustration of my traveling partners whom I met on the way. But stick to your guns and don't take chances. A trip through Africa is not the place to take big chances. Do that at home, and then know what you can do and especially what you can't do.
And then there are the usuall "why would you want to do it fast" replies. Another version is "why don't you just drive up and down the motorway for a couple of weeks and save yourself a lot of trouble". For some reason these people think me (and apparently also you) a lesser worthy traveler if I don't find enjoyment in camping in a village for several days and get to know the local people. Or generally go to great lengths to make things difficult for myself by going the less traveled, and thereby more difficult route. The more scrappy the bike, the more meager the equipment, the smaller the budget, the better in these guys oppinion. Doing it fast (or fast'ish) and on the main routes all the way through Africa is an achievement most people only dream of, and only few actually get to do. I wish more power to you. There are plenty of things to see and experiences to be gaines if you stick to the "main route". You will still find yourself driving in worse conditions on the main route than you will propably find on your local off-road track at home. Just because it's a main route, doesn't mean that the road is good. Especially in central Africa.
If you wish to contact me regarding more specific routes, I'll be happy to give you a few suggestions. I can also supply a few waypoints for your GPS that you might find usefull (some embassies, campsites, hotels and such). My mail is firstname.lastname@example.org
. I only occasionally drop into the HUBB so it is likely to be a while before I respond if you send me a PM using this sites message function.
As said before, regardless of your route, the trip will give you a great many experiences that you will remember for the rest of your life. This can, in spite of some peoples oppinion, also be achieved on the "main" route.