Regarding your example about 100k and 20k 401k vs taxable 120k, it's probably not fiscally responsible to choose the latter except for certain fringe cases.

Without going into the deep financials, it's much easier to live below your means now in your 20s then when you are raising a family later on in life. It would therefore be wiser to live below your means (even if this means living like a college student in San Fran or NYC) and choose 100k, be relatively frugal, and put away that extra 20k without tax. Starting a solid 401k in your early 20s is one of the most fiscally sound decisions you can make.

I don't mean to criticize your reasoning, I'm just offering another perspective.