Where are you coming from? Which costs less, flying to Jackson and renting a car or flying to Kalispell and renting a car for the same amount of time?
What haven't you seen in Yellowstone? What haven't you seen in GTNP? What do you think you need to see again in either?
Now that the GTTS road is open all the way through over Logan Pass, this would be the time to go to Glacier and spend 3 full days there before heading south to Yellowstone for 2 to 3 days and then returning the rental car to Kalispell airport.
For lodging on the west side of Glacier I like Meadow Lake near Columbia Falls. There is quite a bit of lodging available at East Glacier but I don't think it is as high class as Meadow Lake.

Thanks! Originally, we were taking some family members to Grand Tetons and Yellowstone for the first time, but plans have changed and they can't come anymore. Our plane tickets were already set, otherwise we would have taken a different flight path. Thank you for all your advise, perhaps it's indeed a bit crazy to do all of that drive within our time frame and flying into Jackson. I will keep your tips for our next trip. Happy travels!

And on that note- since this will be our 3rd trip, do you know any off the beaten path nice trail in GTNP or YSNP, that's not too long? My 4y/o can make 3-4miles of hike himself, the rest we would have to carry him. Thanks!

Do you have a copy of A Ranger's Guide to Yellowstone Day Hikes? We picked one up on our first trip in '03 and found it very helpful. Hikes are ranked according to difficulty, you can check the mileage, and there are 4 or 5 pages of description of each hike. They still have the books in the Yellowstone bookstores, though I imagine it's a more recent edition. You might figure that hikes published in a book aren't so off the beaten path, but we never saw another person on the ones we have done. (Of course, we also go there in shoulder seasons - early Sept. or early June. Don't know how much difference that would make.)

Speaking of never seeing another person, although we have not bothered before in Yellowstone, we did get bear spray when we were in Yellowstone earlier this month. With the events of the last two years in the Yellowstone area, we decided it might be a good idea. As it happened, the cold and rainy weather dampened (pardon the pun) our enthusiasm for too much hiking this trip, but we did see a lot of bears - mostly blacks but more dangerous, one with cubs and some grizzlies) from the roads. First time we have ever seen bears there. (Previous trips were early Sept., so don't know if the sighting of bears was coincidence or seasonal.) And we certainly had bear spray at Glacier a couple of years ago. We picked ours up this year in Casper since we were driving from the Black Hills and paid $32 including a holster, which was cheaper than we paid in Glacier; we saw the identical brand and size, sans holster, in YNP for $62. So I'd check outdoor stores in Jackson.

Don't put your bear spray in your suitcase when you go to fly home. You will have a problem with TSA.

We give ours to the rangers - suggested by someone on this forum before we went to Glacier. Earlier this month at Y'stone I noticed signs (maybe something in the park newspaper) about the bear spray "recycling" program, so now leaving it with a ranger when you leave is an official suggestion. Suppose with budget cuts and Wyoming bears behaving badly of late, they can use the extra spray.

Good that you mentioned it, though. I believe it used to be iffy to take it into Canada, too, but I think maybe it's okay now. (We took ours on a day trip to Waterton when we were at Glacier and if it wasn't legal, at least we didn't get caught.)

Driving UP to Glacier NP is not a problem. Driving UP and BACK and seeing anything other than Glacier would be a problem in that time frame. But if you are willing to drive that far it would be worth the trip and we can recommend stops along the way. Trying to fit in YNP, GTNP and GNP with the round trip drive? No.

The only way I'd do it would be Day 1 - GT, Day 2 - YNP, Day 3- drive to Great Falls, Day 4 - Drive to East or West Yellowstone, Day 5 and 6 Glacier and start drive back, Day 7 - Drive back to Jackson.

Thanks everyone! We do always take bear spray as we saw 4 black bears and 1 grizzly the first time we went, and 4 black bears and 2 grizzlies the second time (about 50 yards away, too close for my comfort even though we were within a group). I have a lot of luck spotting bears, even saw 2 in Big Bend NP! I take no chances...I'm glad they are finally recycling the sprays. I know they are double the price inside, but I hadn't thought of looking in Jackson, will do that this time. Thank you for all the suggestions, wonderful! Gotta find that book.

Well, at least you spot the bears. We are more concerned with alligators, especially when we're engaged in "bird-watching light" (no life lists, just interesting behavior among wading birds large enough to spot easily or eagles and hawks). As we wander through the (often man-made) wetlands, I constantly find myself getting way closer to gators than I would like before I see them. Have some fear that I might stumble across a bear the same way.

Of course, I live about 4 miles from the neighborhood where the bear wrestling incident that was on the news a few days ago took place - and where the woman was bitten on the rear end while taking out the garbage a few weeks ago. These things used to be rare and happened 30 miles away. Maybe I won't have to go to Yellowstone or Glacier to stumble on bears.

http://www.youtube.com/watch?v=TRDCLcVGmUE