Who uses Tanks instead of Infantry?

I use Heavy Tanks over Infantry all the time since I have infrastructure and ICs in every resource producing province

Well Infantry is extremely helpful I mostly like to use air. Infantry is mostly useful in cities and and I use Light tanks to take flat areas after I carpet bomb them.

I don't use infantry all that much i morely use light tanks with some sort of anti tank along with artillery and air support, I might make one batch of infantry at the start if the game just to boost numbers.

I sometimes use infantry with my artillery stacks. But armour is better for defence generally as it can defend better from infantry. However, if my enemy uses lots of AT/TD then I will use infantry as my HP fodder troop for artillery.

Generally I don't however use infantry much, and use tanks for HP fodder and not for any offensive actions except maybe for taking land. But not for melee as they really tanks / no unit is great for melee compared to arty/planes.

In my first few games, I leaned heavily on LT's. But after often going low on oil, I started using a mixture of both LT's and infantry- mostly artillery and AA with some AT. Add a few planes and naval units and you should be doing OK ...