Six of One, As Little As Possible of the Other
As you note, there is minimal difference between I-74/I-70 (Indianapolis) and I-71/I-74 (Louisville) in terms of either miles or time. But having driven both, I would give a slight nod to the Louisville route simply because you are likely to see a shade less traffic and the route suits my tastes better. Your tastes may be different.
By the time you hit I-605, you'll already be well within the L.A. basin and the attendant traffic which you should start to notice near the intersection of I-15 and CA/I-210 in Rancho Cucamonga. If you really want to avoid all traffic, I'd pull up as soon as you get to this area.
AZBuck