IUI Vs. IVF

What are the success rates with IUI and IVF?

Why would a doctor recommend one over the other?

I know IUI are a whole lot cheaper too.

Is IUI good for men with low sperm count and motility because it’s brings the sperm to the uterus? So it doesn’t take that much work for the sperm to meet the egg?

Any input would help :) btw I’ve only been TTC for a couple of months so I’m not quite freaking out yet but it’s just good to know these things I guess