I have both. Had Carrara since version 1 and C4D since v7. I now have the latest versions of each - C6 Pro and the new C4D v10.5 XL Bundle. It does really some doen to what you want to do in computer graphics. If you are a hobbyist and just playing around every now and then then C6 Pro is great. If you want to do professional work (not that it can't be done in C6 Pro) and need more versatility then defintiely get C4D. It is amazing software, straightforward to learn, and has pletny of learning resources available. The rpics is also a major issue. C4D is ore expensive whne you get into the XL and Studio Bundles...but in my opinion you do get what you pay for. Their modules like MOCCA  and Hair are amazing.

Bottom line is figure out exactly what you will need the software to do and that should tell you. If still undecided, get the demos.

Best of luck....and btw, there is no right or wrong choice, it is what is right for YOU!