Between mechanized and motorized, you need to pick one and stick to it
I usually go with motorized for the following reason :
- You can start motorized tech way earlier, when you have less things to develop. By the time Mechanized arrived (day 20), I have already a lot of motorized around,
- Motorized is weaker against almost everything than mechanized, BUT mechanized is crippled against anti-tank and there is no other units than motorized / regular infantry / commando to do the job, so motorized do the thing tanks can't do, mechanized do the same thing as tanks and can go in cities...
There is also a key-ressource constraint :
- Mechanized needs steel. Sometimes I am good on steel, quite often(naval games in particular) I am low on steel,
- Mechanized need more oil, something else you need a lot for, well, all your other units except commando, artillery and AA
- Finally, mechanized needs the same amount of wheat or more if you take into account that you need to build and maintain level 3 barracks around, barracks that you won't be able to "keep at level 2" if you used the province to build something simpler...
In a nutshell, mechanized use ressource you need, motorized don't use ressource you need, so you can get several times more motorized than you would mechanized. If you have infinite ressource, well who cares you have probably won already.
Finally, it makes sense to have motorized max level and mechanized level 1 for damage mitigation purpose, and level 1 mechanized is good in itself. It makes less sense (and is way harder) to have max mechanized and level 1 motorized, since a level 1 motorized is quite weak by the time you have mechanized.
In practice I would max motorized until day 20 research mechanized, and then depending on ressources, number of existing motorized fleet, existing level 3 barracks (in general = none) and how much anti-tank and similar I expect to meet I would focus on either mechanized or motorized from that point onward.