If by easier you mean fewer high mountain passes, I would say I-90 is the easier run. Stick to the interstate and you won't encounter anything steeper than a 6% grade. However, those grades can be very long (like 10 miles sometimes) and are tough on equipment. I can't tell from your post what rig you will be driving but take care of your brakes on the long down grades (don't "ride" them, use short firm application, keep your speed down, use lower gear). Keep your engine cool on the long climbs (lower gear, lower speeds).
If you really want details, get a copy of Mountain Directory Guides . Check out their website then order a copy if you think it will be helpful..
Tom & Jan
Full timers since April '06 - 1 fur kid (Archie - mini Poodle.)
2006 Beaver Patriot Thunder towing 2012 Subaru (4 down)
Started workamping Sept '07 - "This isn't too bad. Think we'll do it some more."
Just for laughs and giggles, you might drop down to US 20 - longest highway in the US. Runs from Newport OR to Boston MA, coast to coast. It is the E-W highway through Yellowstone, than on to Cody WY and so on. Last year on our return from AK we came down from Glacier NP to Yellowstone and drove US 20 straight through to Rochester NY. In IL we did jump off onto I 80 as surface roads through Chicago did not seem the wisest idea in a 36' coach towing.
Lots to see along the way and very little traffic. Iowa was a bore, mostly (sorry to you Iowans, but it was our experience). Great free and cheap town parks for camping along the way.
Trucking down the road in our Phaeton 36QSH on Freightliner Chassis with a Cummins 380 pushing it. 2011 Cherry Red Jeep Wrangler Rubicon with US Gear Unified Tow Brake System. Check out my blog
FMCA 352081 SKP# 99526
No question I-90. Pretty easy drive. I-90 in eastern Minnesota was horrible but I think they were working on it. Not sure if construction is finished. Perhaps someone knows. You could drop down I-35 to I-80 to Illinois as well.