I am a C# programmer who started using ubuntu about 2 years ago. I'm wanting to learn GUI programming in either C or C++. I don't really like mono, it tends to crash on my system. I have a basic understanding of C++. I have never worked in C, but it looks cool. Which toolkit should I learn/use? Give Pro/Cons of each. Thanks!
Since C++ is more familiar to you, you may find GTKmm to be a better fit, since you can use idioms like RAII. Unfortunately, GTKmm is a little incomplete and is missing a few of the lesser-used parts of GTK.
GTK+ on its own, however, essentially exposes an object model similar to what you find in C++, but with only C functions. Things like construction and destruction in C++ are done explicitly in the C API and instances of widgets are handled via pointers exclusively.
Try both and see which fits your project better.