I use both a pencil eyeliner as well as a something called a eyeliner pen which is basically just like liquid. I think the easiest to use would probably be a pencil -.- Buuut you can always learn to use a gel eyeliner. Just watch some online tutorials :))
I usually wear eyeliner on my top eye lid quite heavily and like making the whole eyeliner wing thingy on the ends of my eyes. I honestly do this like every day and am addicted to the eyeliner on top lid look. Makes your eyes look crazy pretty ^^
revlon eye liner pencil with pencil sharpener and smudger and maybelline gel eye liner. I have used liquid eye liners and I find those the most difficult to use for beginners. When i first started using eyeliners, I started with a pencil. more specifically this kind: http://pics1.ds-static.com/prodimg/36358/300.jpg
I found it gave me easier control to use. Once I got used to that I moved onto gel eyeliner. My reasons for that is I have oily skin and I feel gel just lasts longer with minimal smudging. Now if you want a tip on applying eyeliner and creating a winged look, this is the video I learned from: https://www.youtube.com/watch?v=TkCv_oLTTTk
Now she uses liquid eyeliner, but you can use the technique for any kind of eyeliner. Hope this helps!!
I believe the easiest to use would be the liquid pencil eyeliner. I've never tried gel eyeliner before to be honest. I am sure it will be easy enough to learn though. There are many YouTube tutorials that can help you out if you're willing to learn how to apply it. As for the style... it depends on my mood. I usually wear it on my top eyelid though!