Mine is from Winterhold to Windhelm, cutting SE after Whistling Mine then following the cliff/mountain line south, jumping onto the wharf dock and into Windhelm. No more Fort Kastov!

Yours?

I use that same route.

While not exactly the same, when I leave the main gate of Whiterun, I don't follow the road to the right and then the 180 that leads to the stable. Instead, I go straight (west) and jump the wall, landing on the large boulders.

I'm sure that isn't unique, though.

It'll have to be the mountain-passes. The scenery is breathtaking.

Riverwood to Whiterun is a nice short cut. Take the path towards the barrow and there where the wolf is, cross down over the rocks. You'll come out down the hill by the farm.

I also leave the whiterun main gate and jump down the wall and land where the khajiit caravan usually camps.

I usually go into Embershard mine through the unmarked exit and come out the marked entry. Not sure if that's a short cut.

whiterun to ivarstead/High Hrothgar from stormcloack camp going into the mountains and then straight to ivarstead

Instead of taking Farengar suggestion of going to Riverwood and then proceed to BFB, I go to a path near Secunda's Kiss that is much quicker.

For Hircine's quest, I take a path near Brittleshin South entrance and follow a path and go towards Bloated Man's Grotto (there is a silver ore vein or two)

*this one I learned from Resident* Instead of going to Ivarstead from Helgen, there is a better, peaceful path near the Ritual Stone (north of Whitewater Watch very near Stormcloak Camp) that basically eliminates a bit of headaches (iirc, just a troll near Ivarstead which you can sprint away)

**got ninja'd on this one**