Both the Sony STR-ZA2100ES and the Pioneer Elite VSX-LX305 are solid choices, especially at the $300 price point. The Sony is known for its clean design and reliability, while the Pioneer offers a rich feature set, including advanced room correction and streaming options.
If you're planning to expand to Atmos in the future, the Pioneer might offer more flexibility. However, if you're satisfied with a 5.1 setup and value straightforward operation, the Sony could be the way to go.