Differences between Tiva C series & MSP430

Really, the best way to compare the two would be looking at their datasheets.  The simple one-liner would be that the MSP430 has better power numbers at the cost of functionality and pin count.

The architecture between the two is very, very different.  The TM4C uses a 32 bit cortex M4f processor, compared to the 16 bit RISC mixed signal MSP430.  The TM4C you listed can run at 80 MHz, the MSP430s run around 16MHz.  I don't think I can effectively illustrate the architectural difference between these two in a single forum post... If you want an in depth understanding of how the ARM M4 is different from the RISC on the MSP430, you're going to need to do a non-trivial amount of data sheet reading.

I personally feel that the software libraries for the TM4C line are more approachable for someone new to microcontroller code, but my mind is infinitely biased by the fact that I had been working with Stellaris and other ARM MCUs for years before I had any incentive to investigate a 430.

Again, personal preference from a guy who is paid to write code for the TM4C, but I feel that the TM4C has a wider range of portable sample code and peripheral example code than the 430 (take that with the appropriate grain of salt).

For support, you will likely receive similar, (hopefully) excellent support on either device from their appropriate forums and TI sales representatives and Field Applications Engineers.

For community, the MSP430 has a larger user base, so you are more likely to find random DIY projects and forums discussing the MSP430 than the TM4C line.

If you have questions about a specific area of functionality, I can go into more depth (as character limits and my admittedly limited knowledge of the MSP430 allow), but I would advise against trying to figure out which of the two MCUs is "better."  Different applications have different requirements, which in turn have different ideal part selections.