I think finding a really good eyeshadow primer can be difficult, but there are a couple out there.
I try to figure out just how often I’ll actually wear makeup on the trip and how much/dramatic it will be. I then try to take light and dark shades from various product categories so I can always mix to get something in the middle.
For me, it depends on the feel of the brush itself. I’ve used great brushes from both camps, but I’ve also found scratchiness from both.
It’s all about opaque color in one stroke — I don’t want to have to go back over the same line to fix any unevenness. It should stay on for 8 hours or longer without fading or migrating!
Creamy enough to glide on and deliver opaque color in one stroke without drag but not so creamy that you end up with smudges beneath your eye an hour later. I like twist-up mechanical pencils best, just because you don’t waste product by sharpening.