Thank you all. Sorry for coming back so late. My main interest in features would be speed, fast/high resolution timers (for input capture) and good ADCs. It should be an IC to put on my own boards rather than a little module though if both are available it will typically be better for finding support and examples.
I also want something I can get easily from reputable suppliers like Farnell in the UK or maybe Mouser.
I have seen the SAMD51 series seems to suit my needs and there is also a dev board from Sparkfun I can practice with. I am wondering though about the clock speed and how you run it at 120MHz. I can see in the Sparkfun schematic they use a 32.768kHz crystal oscillator.