All depend on price....? how much is 4 1660s and 1 3090?
If it is same price of course 3090 better, alot gpu means alot headache.
Alot of headache and more money to spend on risers too, probably even power supply, a single RTX3090 don't need two but one PCIe x16 slot and one motherboard too, very easy, go for the RTX3090