Just reading through this along with Todd's link as well, and although we have only done 2 trips to Glacier so far it got me thinking how difficult this question is to answer. Truly the answer is whatever trail you happen to be on at the time.
Each trail offers it's own magic, it's own uniqueness.
I love Grinnell Glacier, I think it has it all. Alpine vista's, waterfalls, Grinnell Lake, the chain of lakes, and of course the glaciers.
Siyeh really captured my heart this year. So diverse! Again a bit of everything on this hike. Preston Park, waterfalls, views that take your breath away, glacier, gorges, WOW! I'll never forget the false summit and my "holy S--T! Well when you go over the pass and see that trail below you it really makes you wonder what you got yourself into, BUT OMG I would repeat this one over and over again too.
As I am becoming a Glacier addict, I'm finding the hard part to figure out which is the "next" hike, and which ones you have to try to pass on repeating. I don't know if I could ever go to Glacier and not do HIdden Lake, that short hike is just breathtaking! Makes me feel like I am in the Alps!
Iceberg Lake, the un-named meadow and little lake (I decided to call it Meadow Lake) just before the lake and the color of the lake itself... WOW!
I know Avalanche gets alot of negative reviews, maybe it is because it was our "first hike in Glacier", but I think the destination is very special.
Dragon's Tail this year, although we did not complete it, the views from the first saddle were outstanding.
Again each trail has it's special characteristics that imprint upon your memory forever!
Such a speical place! My dream is that one day I can do what Chip did this year, and share it with our girls.