I will start with the worst ones...
This is Craftsmart by Michael's. One time I came across one that really worked well, but lately I bought two that are AWFUL. You push the nib down and expect to get a good flow, but you get a huge blob and no flow. I'm taking them back. They were $3.99 or $3.49 (can't recall exactly.) This pen does not work well on canvas either if you're trying to outline something.
You would think Prismacolor would have a great pen, but this does not work on paper, or any other surface. Just don't buy it.
Pen-touch by Sakura. It's goes on in blobs and it's hard to use. I regret buying that one, and I don't remember the price.
Gelli Roll pen works ok on paper with a very thin line. Great for doing fine work and outlining. Good flow and lots of pigment. Doesn't work on canvas.
I used to LOVE Elmer's Painter's pens. I would buy the box of various colors when I had a 50% off coupon. They lasted for a long time and the paint spread consistently. The white worked like a dream. The quality has gone down considerably in the last two years. I'm so disappointed. They don't last, and they spread blobs too. You start a line and it's ok, but fizzles out after a couple of inches. I have not seen an improvement in the quality, so I'm going to quit buying the brand. I didn't have a white pen to use in the picture because I threw it out in a fit of frustration...lol.
The Faber-Castell pen is good. The only set backs: the nib is thick and you have to apply the lines a couple of times to get a solid white line. But it spreads evenly without blobs.
DecoColor also spreads a good line, but you have to apply a couple of times to get the solid line. It also smells vile of chemicals... I aim my fan toward the table when I'm using it.
The winner is: Uni-ball Signo. It draws a really good line, but is not permanent. Unfortunately. For paper work it's great, but not on canvas if you're going to apply something else on top. It smears. I did get a whole box of them for $23.00 at Jetpen's and if you buy, make sure to get the Japanese version. See the lettering on the box? Free shipping if you spend $25. I had some of their other colors as well, and they are great for writing, so smooth and easy.
What is your experience with white pens?? I would love to know since I'm still hunting for that perfect PERMANENT marker.