There are quite a few directions for this, and to be honest it all comes down to a desired usage and workflow. In all cases if you dont have a reasonable Tablet pen then stay inside C4D for sculpting as its not half bad.
Lets say your making a monster and have no set concept, then the last thing you want to be doing is making a base mesh in the traditional way as the base mesh dictates your design choices too much. This is where another sculpting app comes in as there is no way at this time C4D gives you the freedom to explore your design choices fast. Now I dont know if 3Dcoat has some kind of way to develop a fast base mesh that starts the process off for conceptual work, but Zbrush does with Zsphears, shadow Box, and Dynamesh. Here im talking about getting down ideas from your head into 3d as fast as you can think of them by removing all technical restraints.
What if your concept is great, and you wish to take this to the next level specifically for animation? Your have 3 choices, use your concept as a background guide to build a 3d model from using traditional methods as a background image set, model around it in 3d space, or re-topologize it. The first two choices any sculpting app can do, but re-topology would be directing at 3Dcoat, as Zbrush re-topology tools are not as good. If you need to get an additional re-topology app then this bumps the cost up for the process, unless your happy to do this in C4D. I use MODO for re-topology in this scenario.
There is also the case that your concept sculpting may need a fast render preview to help direct your concept choices. 3Dcoat has PBR Zbrush has BPR, but Zbrush has the option to expand its renderer to Keyshot 6 Pro limited to Zbrush which cost a fraction of the price as the open version but all the features are the same. This gives you a very, very high end render engine in which is linked directly to ZBrush at a click of a button millions of polygons are sent to Keyshot in hardly any time. If your a concept artist you can make your mesh, concept, paint your design and render it in Keyshot for a final image in which your never have to even open C4D.
In production for animated meshes things change a bit, as you may come from the direction of already having made your base mesh in C4D, in this case I cant see why 3DCoat will fulfil your needs from that point onward, however your need to look into how good, and easy the process is to produce displacement, and normal maps?
The digital sculptor whos artistry is in producing clay like sculptures, and who wants to feel they are in contact with clay, then Zbrush all the way, nothing feels like Zbrush in the response you get from the brushes, this alone for me would direct me to Zbrush as thats a area thats very important to me coming from a traditional sculpting direction.
If I was in your position id have a good think on what your direction and work flow is, and your budget. I think for general sculpting C4D is brilliant.
Dan