Seems completely workable. I've done the loop a few times, most recently in a single day (this was last week–I posted a trip report in the trip reports forum, if you're interested in more details).
My $0.02 on your trip:
I would probably stick with Day 1. It's a 15.5 mile day or so with 5,000 feet of climbing. For many, that's a pretty full day. Plus, if you're coming up from sea level, 8,500 ft is a pretty good place to spend the first night. The risk of any altitude issues is pretty low.
I'll call yours TRIP A. The following are alternatives I'd consider for the next two nights:
TRIP B
Day 2: Ascend to Rae Lakes, then enter Sixty Lake Basin. Explore Sixty Lake Basin, then exit, to camp at Rae Lakes. This will amount to about 14.3 miles, and +4,100 ft, -2,000 ft. In other words, easier than Day 1 in every sense. This allows you to explore Sixty Lake Basin (which is spectacular), take in views of the Rae Lakes trail from the Sixty Lake Basin trail (also spectacular), and spend more time in Rae Lakes (one of the highlights of the loop).
Day 3: Rae Lakes, over Glen, to Road's End. This is a slightly harder Day 3, but your pack will be lighter, and you'll have your "trail legs". 18.6 miles, +1,700 feet / -7,300 feet.
TRIP C
Day 2: Ascend to Rae Lakes, ascend Glen Pass, descend to Junction Meadow, and ascend to East Lake. East Lake (and Lake Reflection, if you have more miles in you) are highlights that are so frequently missed on this loop. Google image search "East Lake Kings Canyon" for a sense of this. Day 2 is now 17.7 miles with +5,254 feet / -4,293 feet, which shouldn't scare you after Day 1.
Day 3: Simple descent to Road's End. I didn't bother looking up the numbers–it'll be quick.
If you're unfamiliar with Sixty Lake Basin or East Lake, I can send links to maps, but they're both on Tom Harrison maps, NPS maps, and the USGS quads, so I suspect (hope) you can find them.
Lastly, if you're uninterested in the options above, I'll give you my opinion regarding your original question:
Both are fine. If you want to get out quicker, descend to Junction Meadow. Otherwise, I think Vidette is a little more scenic.