The buses can be utilized to visit most towns and villages. There are stops along the way, but the next bus passing by could take quite a while. If any of those will be your actual destination, know that some buses might only run 2 to 4 times a day. Weekends have less service. This would be my last recommendation for exploring, because it is an inconvenient way to travel in many different aspects. Looking over and trying to decipher the bus schedules gives me a headache.
Car rates should be very economical in March, even if you reserve for the entire week. This is the optimal way to explore all the islands (except for Corvo),and what I do for every trip since 1994. There are plenty of safe and free parking lots in Ponta Delgada.
In my opinion, the Azores islands are the safest places to visit in almost anywhere in the world. You should not feel any apprehension driving alone around Sao Miguel. Almost all roads are paved. In the cities and villages, many roads are narrow. Navigating is easy with your smartphone map.
There are probably dozens of car rental companies on the island. They all have positive and negative reviews. Most have more negative reviews than positive ones. Use due diligence when reserving and picking up the car.
I explain just about everything you need to know regarding renting cars and driving in the Azores. That chapter in the free sample of my guidebook. At the top of this Portugal forum, the webmaster wrote a post with the link to my book. From there, just download the Kindle app to your electronic device to read the free sample (the first 52 pages). The is NO obligation to purchase the entire 533 page Azores guidebook if all you need is in those free pages.
I will say while driving to be extra alert for herds of cows walking on the streets and moving to different pastures, the inevitable fog and rain, and dimly lit roads at night. Probably the cows will be the only factor you generally do not encounter when driving at home.
I hope you have a wonderful trip!
