Really depends on your interests. I frequent several programming language/platform specific and photography subs, plus r/mechanicalkeyboards, and several from my local area.
Reddit's multisub feature makes grouping them easy (so I visit six places instead of 40).
The ones I frequent include financialindependence, headphones, coffee, mealprepsunday, running, bicycling. They all tend to cater to their audience fairly well.