I vote for tax simplification. When I started in 1973 with IRS audit, we did all our computations by hand with pencil and paper. Easy peasy.
When I left, no one could use paper and pencil since it was too complex. People on the counter were even formally trained in each area and never allowed to answer any! question not in their direct area no matter the simplicity of the question. They would be written up. They had scripts on the computer for answering the questions that went on and on to try and identify each and every permutation that could arise from even a simple question. If they missed something, again written up. Plus there were areas that none of the counter people were trained on since the areas were deemed "too complex". Customers were directed to the phones. Some is understandable. There are accountants making 6 figure salaries trying to make complex decisions and a counter person making $25,000 can hardly be expected to "know everything".
I even had people in my own office refuse to answer a question from me and we both worked there and it was a business related question. I was steamed and they heard about it.
So my peeve is tax complexity.