There are currently these 15 Ukrainian Light AFV's (inc a truck and car) in the game-
I compiled this "shopping guide"-
The purchase screen. The far right column is the increased cost when rarity is set to "Standard"-
Note- I've seen 14.5mm HMG's engage main battle tanks, usually while auto-reversing.
They also engage light armour and usually kill it with several bursts.
The BTR-4E has got ATGMs, 30mm cannon, Grenade launcher and MG and i've seen it fire all of them at different times at the whim of the crew.
The BRM-1K has got a low-velocity 73mm gun which misses by a mile at longish ranges, but is useful for lobbing HE shells at infantry.
We've all got our favourite toys, personally I use the BTR-70 for getting troops from A to B, it's more expensive than a truck but it gives the troops protection against small arms and shrapnel all the way, and packs a useful 14.5mm HMG to dish it out.