So for... reasons... Microchip has seemingly killed off the "ATTiny" and "ATMega" names. But modern AVR chips continue to be made in the form of AVR DA, DB, DD, and EA. I don't know why Microchip thought it was a good idea for a namechange after decades, but its not a big deal, we engineers can figure out the new naming scheme, right?
The main advantage is that 24MHz is supported at all voltage levels now, allowing for more battery efficient loads. Furthermore, there have been significant changes to the Timers, UART (now a USART), and other such I/O.
That being said, AVR DA supports up to 128kB Flash + 16kB of SRAM, making these chips far larger and more competitive.
AVR DA's killer feature is the PTC / Peripheral Touch Controller. Capacitive buttons require a fair amount of smarts to measure capacitance (ie: inject current and measure the speed at which voltage changes), and PTC automates that process. This is an old, obscure feature of ATMega328 however, but it seems like Microchip wanted a specific AVR to offer this feature. The other three lines do not have PTC.
AVR DB's killer feature is 3x Rail-to-rail OpAmps. OpAmps are the old 1920s style of analog computers, where your values are stored as voltages. Addition, subtraction, multiplication, division, exponents, derivatives and integrals can be done on these difficult to use Operational-Amplifiers. But more imporantly, a fair number of "analog circuits" use them to amplify voltages to usable levels, or improve current/voltages and provide better measurements.
AVR DD is a bit cheaper, but offers multi-voltage I/O. PortD runs off of a second powerline, meaning you can have a 3.3V PortC, but 5V PortD. Its basically an integrated level-shifter.
AVR EA is thew newest of the bunch and seems to be the cheapest / fewest set of features. I'm guessing AVR EA (or maybe even "E" line entirely) is the new ATTiny, while the D-line is more akin to the ATMegas.