I like eyeshadow better bc I have light hair, eyes, & skin and lighter stuff just looks better on me. Eyeliner always ends up looking too dark.

I usually use eye shadow as a liner. I get my eyeliner brush wet and swirl it around in the shadow (though there are products out there that you can use in place of water that make it stay longer). Usually I'll use an angled brush to take a bit of that shade across my lash line to smudge it a bit, then wet my liner brush in that same shade to give it a bit of definition.

If you have short eyelashes, glasses, and smaller eyes, then eyeshadow won't matter quite as much as eyeliner.  I go for deep purple because it  brings out brown eyes, whereas brown disappears on me.  I will use other colors too, on my upper lid if I am not in a rush.  If I look in the mirror without eyeliner, there is more of a difference.  I think more people are into mascara than eyeshadow and I don't get that.  I do not like mascara as much due to, it may smear, run when you tear, and does not show up as much on me too.   I guess if you have light eyelashes it may really change your look, but on me, I choose the eyeliner first.  And yes, some of them (lighter colors) look great in eyeshadow techniques too. 

It makes my eyes pop

I like them both, but I switch depending on the time of day and/or occasion. A lot of times I like to wet an angled liner brush and line my eyes with wet shadow for an intense and more colorful line if I feel like going for a more fun look. I own a lot of colored liquid eyeliner already, but sometimes I'd prefer to use a color that I wouldn't be able to find in a liquid form, so I use shadow. 

Sadly, i can't wear eyeliner. Everytime i do wear it, i look like a raccoon. I stick to soft shadows instead, since i try to lean towards natural looks.