Although this is our own personal opinion, we strongly recommend to always use const auto& when possible, this communicates that you simply just want to fetch a value and that nothing fishy is going on. This should be the case to the majority of the variable declaration in a C++ code base.
auto& and auto should only be used when you require the behavior of a mutable reference or an explicit copy; this communicates to the reader of the code that those variables are important as they either mutate another variable, or they might mutate another variable if not copied. Finally, use auto&& for forwarding code only.
Following these rules makes your code base easier to read, debug, and reason about.
It might seem odd that while we recommend ...
