You won't get C3 for free. But since it's a long way off, I suggest you don't wait for that to release. Go and buy C2 if you feel like it suits you. Give the free version a try:
Regarding Unity vs C2: In short, developing is much faster and more fun in C2 in my opinion. Search the forum, there has been numerous threads comparing the two engine. There you should find every answer for your questions regarding this topic.