For mazda 3, at about 120k expect to do struts and wheel bearings. My 06 is an AT so I can't comment about the clutch.
For the first gen mazda 3 (04-09), I would get the 2.0l engine instead of 2.3l. The 2.3l has a a cartridge oil filter and a plastic housing. The housing is known to crack easily when over torqued, followed by a quick loss of oil. Most of the engine failures reported on Mazda Forums were caused by the cracked housing.
The 2.3 also has a counterbalance shaft that is known to fail. Not to mention it's quite thirsty for the displacement and HP it produces.
The second gen (10-13) was really a refresh, but the 2.3l was replaced with a much better 2.5l engine and from 2012, you could get a 2.0l Skyactive engine in mazda 3. So that gen can be had with 2.0l, 2.5l and 2.0l Skyactive, which is a direct injection engine. But the smiley face look is not for everyone, although in darker colors it's much less pronounced.
The 3rd gen (2014 to present) is an all new design done solely by Mazda. The other two gens shared a lot of parts with Ford. From what I read, these are also very solid economy vehicles.