I have been using UC3 for previous projects in the past and also wanted to use the UC3 in future.
We are starting development of a new device now. Basically we need to be reading sensor data ( about 6 sensors, 3 via USART, 3 via ADC), communicating over 2-3 Bluetooth connections (mostly appear as another USARTs to us), driving a TFT LCD, writing data to an SD card and doing some relatively low-demanding calculations. There will be also 1-2 device on SPI and I2C interfaces connected. I will also read about 4-6 buttons available to the user.
I will probably have to multiplex heavily or use additional UC3 chip to collect all the sensor data as the UC3 does not have enough interfaces for this task.
The device is battery powered and needs to have low power consumption (such as UC3A0).
I am quite happy with the Atmel Studio and the development tools for UC3 and I am also happy with the FreeRTOS on the UC3.
However, knowing the UC3 is an old part from 2005 - 2010 (anyone knows how long will it even stay in production???) and current growth of ARM-based chips, should I consider moving to such a solution (by Atmel) for this new project? The range of ARM-based chips offered by Atmel is so large I don't even know where to start choosing what might be the best for me (all the Cortex M0, M3, M4, A5 options etc. etc). What could I gain by going to ARM? Most importantly - is it the more future-proof device compared to UC3? Will I get significantly better MIPS performance at similar power consumption? Can I get a chip with many more peripherals on it compared to the UC3? Are the development tools any better or worse? Will the device have significantly more Flash and RAM (I have 512kB/64kB on UC3).
To be honest I strongly lean towards just working with UC3 which I am a bit familiar with already. However, I'd like to make a good choice for my new project on which I can run for another 5-8 years at least. My project in my view fits a pretty standard embedded device definition (sensor data collection, communication with a few other chips, LCD and buttons for UI) and I don't need work with multimedia, video capturing or high performance data processing with large amounts of data.