Uncertain of 8-bit vs 32-bit alternatives to AVR32
The AVR is popular because of Arduino. The AVR32, considerably less so, and there are variants of it going end-of-life. It would not be a good investment, given better-supported options out there.
The most popular 32-bit devices are ARM-based, which would include:

STM32 (ST Micro - huge range of choices)
i.MX6 / MX8 family (NXP, also very extensive range)
BCM2837 (Broadcom, used on Raspberry Pi)
Rockchip RK3399

As well as Allwinner, etc. Some of the boards using these adopt Arduino-like footprints to address that mindshare and take advantage of that ecosystem. Others knock off Raspberry Pi (e.g., OrangePi, which uses Rockchip.)
Another popular platform is ESP32 from ExpressIF, which uses a Tensilica core. It's very low cost and includes wifi.
I'm basing this on the number of questions that seem to come up here. I'm leaving out dozens of others, notably MIPS (very old, but still used in a lot of wifi routers, sorry @jonk) and Risc-V types (still kind of new, not popular outside of China yet.)