Mixing & matching APCs

[Wdll]

I guess it depends on your overall strategy and opponents. Can the enemy hit and destroy your more expensive IFV from a large distance and with great efficiency an rate? Do you prefer to have your APCs/IFVs be able to destroy anything larger than the basic APC? It looks like you have answered yourself. If you don't like IFV that can carry ATGMs (I assume typing AFVs is a typo on your behalf), then you might as well go for the cheaper solution and invest the money on other type of units, better infantry or tanks etc.
I like and prefer to use expensive IFVs, but that is not always the best solution. Some times it is better to use a large number of cheap APCs with only a small percentage of IFVs that are used as a backup or there to provide extra attack support if the opportunity arise.
One of my personal favourite units is the BMP-1. Even on it's basic configuration it has good enough Vision, firepower to kill even an enemy tank (but mostly luck against MBT) and better firepower than most Western tanks up to the late 70s-80s. Very good firepower against infantry and against all (or 99.9%) enemy APCs and IFVs.