The CX-3 is quite small and it uses either a 1.5L or a 2.0L

The CX-5 is quite large and it uses either a 2.0L or a 2.5L

with in the SkyActive-G engine family I'd say the 2.5L is the best one, with the 2.0L being a solid second place.

The 1.5L is decent but it has only 114 horsepower and it is the weakest in the engine family.

What I'd recommend in general is going for the medium sized CX-30 with the larger 2.5L engine (non-turbo) but since this model is quite new there aren't many used ones yet.

But out of these two, I'd definitely recommend the CX-5. I believe that in 2017 they haven't rolled out cylinder deactivation yet (a mode that will wear your engine faster) making that car the best option with either engine.

For CX-3, look at model year 2017 or newer.  The engine (naturally aspirated Skyactiv-G 2.0L I4) and transmission (6-speed automatic  transmission) were pretty solid.

https://www.autotrader.ca/expert/20200305/2016-2019-mazda-cx-3-used-vehicle-review/

https://www.motorbiscuit.com/is-the-mazda-cx-3-reliable/

https://www.carcomplaints.com/Mazda/CX-3/

For the CX-5 (which is bigger than the CX-3; you have to decide how much space/room you need) also look at model years 2017 and newer.  For 2018 model year and newer on the naturally aspirated 2.5L I4 engines (only) they introduced cylinder deactivation and had to issue recalls later for 2018/2019 model years with that technology due to issues within the PCM/ECU malfunctioning at a critical point in the activation/deactivation of the cylinders (causing engine to misfire, lose power, stall). It was a software fix, but jury is out on the long term reliability/durability of the cylinder deactivation system in that engine (and no way that I know of in the aftermarket to disable it.  Mazda itself won’t let you disable it - that’d be too easy.)

https://www.motorbiscuit.com/the-most-common-mazda-cx-5-owner-complaints/

https://www.carcomplaints.com/Mazda/CX-5/

The cx3 has a very tiny hatch. You would be better off with the cx5.