I drove my 2003 Mazda Protege into the ground - 250,000 miles and I never did anything to it. Just changed the oil and a few other routine items. Sold it in good running condition to a friend. Still running as far as I know.
My 2015 Mazda3 S is so far just as reliable. No weird problems, just get in and drive. Change the synthetic oil every 7,500 miles. The only thing that's happened is a screw backed out of the sun visor arm mount. Just needed a little loc-tite. It's at 50,000 or so miles so far. I put a lot of miles on my cars and expect them to last, but I also fix anything that breaks immediately and try to do all the useful preventative maintenance. Never been to a dealer since I drove it off the lot, I have my own excellent third party mechanic.
Really love the get-up and go the 185 HP has compared to the Protege, and still excellent mileage to boot. The Skyactiv stuff is a miracle. baby it and get 400 miles per tank. Gank on it for lots of power and get a lot less, but it's fun. It's amazing how much better the car is all around compared to say, my wife's Honda Civic, which is a piece of junk at almost the same price. Interior, exterior, engine, everything.
I'd say any of the current generation years are fine, and as far as the previous gen, they don't get nearly as good mileage but they are nice cars with a lot of get up and go, and have much better visibility due to bigger windows. the only problem a friend has had with those is the at the time optional infotainment display started to crap out. Haven't had any problem with mine.
I bought both Mazda cars new.
-H