ATSAMA5 ARM Cortex-A5 based microprocessors Atmel SAMA5D3 using IAR. Based on the Xilinx UltraScale MPSoC architecture, the Zynq UltraScale+ MPSoCs enable extensive system level differentiation, integration, and flexibility through hardware, software, and I/O programmability. ARM bought Keil some time ago, so maybe that would be the "best" compiler to chose, since it's made by the same company that makes the cores. The demo uses the FreeRTOS IAR ARM Cortex-M3 port and can be compiled and debugged directly from the IAR Embedded Workbench for ARM. If you decide to go for the commercial compilers, you could start with the size-resricted versions of Keil or IAR. If you decide to go this route and you're on windows, have a look at a combination of CooCox (for the development environment) and yagarto. GCC is a bit of a pain to setup, but is unrestricted and free. You need to chose between a GCC solution or one of the commercial compilers. To begin doing something you'll also need a compiler / development environment. 5+ Years of Experience with Embedded System design and Firmware Development IDEs: MPLAB X IDE, MSVS, ARM DS IDE, Eclipse, CCS, Keil, IAR, Arduino, Energia, Xilinx ISE. Olimex makes many boards for many processors. Or maybe it'll be easier to breadboard the additional elements.
If you have an understanding of what type of devices you'll be making, you should figure out what interfaces, peripherals you'll need and pick an evaluation kit accordingly. It is cheap an has an on-board ST-Link interface that can be later used to debug your own devices with an STM32 processor. I have experience with Xilinx, FPGAs, Virtex 5 and Spartan 6. I-jet is an in-circuit debugging probe for ARM and integrates seamlessly into IAR Embedded Workbench and is fully plug-and-play compatible. If you want to just try something out without having anything particular in mind, a good solution would be the STM32VLDISCOVERY. IAR Systems® is the world’s leading independent supplier of development tools for embedded systems.
You could program the processors with ISP, but for that you'll also have to make a special cable, use additional software for programming and you won't have debugging possibilities (you'll only be able to upload the compiled program). They have a JTAG connector, but to use it you'd also need to buy a USB-JTAG adapter. Both of these boards lack an onboard debugging interface.