Riding, driving or flying? If the latter two, it doesn't matter when, as much as where you stay and what you plan to do. Casinos are nearly freezing in summer with their cooling plants keeping them on a scale of comfortable to cold. So, you'll be indoors a lot in July and August. Early mornings are beautiful, though, before the heat sets in. If I was doing any walking, that would be the time.
Riding - another story. I was there in mid-September several times on the bike....both times were fine. Mid-afternoon can still be warm, maybe even near 100, but morning and evenings are cooler and very tolerable for riding.
I don't stay on the Strip anymore - too busy and I really don't like their casinos for play. Not that they are more unlucky than other ones. It really doesn't matter. It's just that my favorite places to eat and to hang out are off Strip, at the Orleans, Sunset Station, Green Valley Ranch, Suncoast or Red Rock. If I were coming in from far out of town, though, and it was an only visit this year, I'd make it easier to see the known sights - stay near the MGM area at one end of the strip, or at the Mirage/Treasure Island end of the Strip. I'd avoid the far north end of the Strip, except to "see" a couple of things there at some point of your visit.
Remember, what happens in Vegas, stays in Vegas. (They are mostly referring to your money.)