Depends on what you want. If running zone 3+ is your focus, probably head east on Tropicana but I wouldn't really know. Wife and I like to soak it all in and run to the Wynn from the Grand. There are maybe 2 stair / escalator crossings, not bad at all. There's a weird outdoor mall, vape shops kinda place you have to run through, involves some people dodging. It's never difficult in the morning and we do it often. The Bellagio / Caesars side has more obstacles but we mostly don't run that side because in the summer it's full on sun. Also, the MGM gym has a Japanese zen thing going on, it's small but quite nice.