I want to write a compiler for a custom markup language, I want to get optimum performance and I also want to have a good scalable design.
Multi-paradigm programming language (C++) is more suitable to implement modern design patterns, but I think that will degrade performance a little bit (think of RTTI for example) which more or less might make C a better choice.
I wonder what is the best language (C, C++ or even objective C) if someone wants to create a modern compiler (in the sense of complying to modern software engineering principles as a software) that is fast, efficient, and well designed.
The "expensive" features of C++ (e.g., exceptions, virtual functions, RTTI) simply don't exist in C. By the time you simulate them in C, you're likely to end up with something at least as expensive as it is in C++, but less known, less documented, etc. (let's face it: compiler writers aren't stupid -- while it's possible you can implement a feature "better" than them, it's not really particularly likely).
In the other direction, templates (for one example) often make it relatively easy to write code that is considerably faster than is practical in C. Just for one obvious example, C++ code using std::sort will often be two to three times as fast as equivalent C code using qsort.
Bottom line: the only reason for a C++ program to be slower than an equivalent written in C is if you've decided (for whatever reason) to write slower code. Common reasons are simplicity and readability -- and in most cases, those are more important than execution speed. Nonetheless, using C++ doesn't necessarily carry any speed penalty. It's completely up to you to decide whether to do something that might run more slowly.