I understand what your trying to ask but your question still isn't really specific enough to answer. Part of it depends on how much adventure you are looking for, whether you just want to make it there and are quite happy to spend the whole time on tarmac. Do the rally organisers specify any sort of route, even at the country level or is it a completely open choice as to how you get there.
Its possible for example to go down the west coast route through Morocco, Western Sahara, Mauritania completely on tarmac. You could probably get most of the rest of the way round staying on tarmac.
Some of it comes down to political / security situation - for example, if you were to leave now, as I understand the situation from the other posts, you would struggle to cross from Algeria to Niger. Therefore unless you wanted a more extreme crossing from Algeria to Mauritania / Mali for example then you would probably by default have to go for the west coast route. However these situations change quite regularly so something that applies today may well have changed in six months and vice versa.
Sorry its not massively clear. If you go on to Chris Scott's sahara overland website, there are some good descriptions of the routes which might give you a better idea.
Good luck and have fun