NAIL ART PAINT
PROS: Is thicker than regular nail polish (depending on the brand), but not as thick as the special nail polish. The nail art paint is usually HIGHLY pigmented due to the intended use. "Stickier" than regular nail polish which usually means a crisper image when stamped. It's usually super cheap. I buy mine from a local beauty supply store and spend $1 for each color. With some nail art paint brands, simple rubbing alcohol will remove a stamped image from your nail without removing your nail polish base color.
CONS: The nail art brush is usually VERY thin making it harder to use. Image plate HAS to be cleaned in between each stamp. Some brands streak with certain topcoats. Some brands dry very quickly.
SPECIAL NAIL POLISH
PROS: The thickest of all three and does make a very crisp image when stamped. Dries slower than regular polish and nail art paint allowing you to work with an image before stamping (example: removing a leaf from a flower with a qtip). Clean up of all the stamping tools is usually the easiest for the same reason... it's sticky but pliable. Also, I find that when I use the special nail polish, I am able to stamp every nail without having to clean the image plate which saves a ton of time and you all know how I love to save time. Simple rubbing alcohol removes a stamped image from your nail without disturbing the nail polish base color (should you want to redo a stamp).
CONS: At $6-$7, this is the most expensive of the three. Because of the cost, I find myself only investing in black and white (these two are a must) and maybe a couple of other colors. A LOT of topcoats will cause streaking/smearing. Follow the manufactures instructions for topcoat application to the letter!
REGULAR NAIL POLISH
PROS: Endless color options!!!! Price is also a huge plus, because most of us can pick up super cheap nail polish from just about any drugstore. Regular nail polish will not smear or streak when topcoat is applied.
CONS: While most of the time you can get a pretty good image stamped...SOMETIMES you just can't because of a particular nail polish's formula. The regular nail polish is very thin. Regular nail polish dries quickly, you must clean the image plate after each stamp. Also, finding just the right opacity of polish is important. Most polishes are pretty translucent (and get darker with multiple coats) so unfortunately there's a lot of trial and error using regular polish. I've had tons of luck with the "one coat, quick dry" polishes that seem to always be on sale at the drugstore. If you mess up a stamp, the only way to remove the image is to use nail polish remover and risk ruining the nail polish base coat and having to do the entire nail from scratch.
I hope that this post answers some questions out there that I'm reading. Personally I ALWAYS have the Konad Special Polish in black and white. I purchase a ton of nail art paint because it seems to fall somewhere in between regular nail polish and the special polish and the price for me can't be beat. Finally, I pick up the quick dry one coats when they are on sale. Oh, I'm also finding that the exact same holds true for the "Fauxnad" image plates. Happy stamping folks.