As bumpy as I 70 is in IN I would still take it. If you're not in any hurry and just want to sight see then by all means go any way you like. By going to Cincinnati you will be driving a lot of extra miles. There is construction all over the country right now and bumpy roads too. I 70 to Denver I 25 N to WY... or get on I 80 in NJ and stay on it to WY. Once you get out of PA both routes are pancake flat all the way to WY. On I 80 you won't be going thru Chicago you will be well below it and that section of interstate is about 10 lanes wide....Go through there early am or after 7pm.....
If you do take I 70 don't take it through St. Louis take I 270 west at Troy, IL back to I 70. Good luck.