I use Due even though I have other reminder options: There is the native Reminders app, Fantastical 2 (which I use for my calendar), and my task management app (TickTick), but sometimes you just want a simple reminder app with lots of options for recurrences, snoozing, etc. Due just does one thing very well (actually two things if you count timers, but I don't use the timers).
Due is attractive and easy to use. It supports setting reminders via Siri and importing from native reminders. You can create recurring reminders, set custom auto-snooze/nag intervals, set different tones per reminder, easily postpone a reminder for 10 minutes, one hour, 3 hours, or one day. It also keeps a log of completed reminders and supports creating custom timers. It supports natural language for setting dates, so you can say "Take out the trash tomorrow" or "Replace air filter on December 10th."
It's one of my most useful apps. I think it's just a one-time purchase of $2.99. If I recall it is possible to use for free, but the free version has some limitations... like you don't get as many options for auto-snooze intervals.
I would add that I make a distinction between task management and reminders. I don't want reminders for the vast majority of my tasks. I only schedule tasks, or set reminders for them, when I plan to complete the task on a specific day/time. Of course I could just use my task management app for reminders, but I like having the separate reminder app for some things. I rarely have more than half a dozen items in Due, but I have hundreds of tasks in TickTick. So while I might get reminders from TickTick, my calendar, etc. I use the Due app for things I absolutely need to do within a very specific length of time. If it's really urgent, I might have it auto-nag me every 5 minutes.