As a user of Shellac and OPI Gelcolor, I have to say both are great products.
Reasons I love Shellac:
1.) ease of removal- takes 10 minutes no matter what. Just wrap n soak
2.) ease of layering- no client has a problem finding a great color
3.) it's the "Coke" of UV polish- everyone labels gel polishes as Shellac. This is due to the INCREDIBLE advertising CND does.
4.) makes doing designs A DREAM. transfer foil works beautifully, glitter sticks like none other, fades are simple, etc. Etc.
Reason I Love Gelcolor:
1.) comes off in one sheet. No pushing is usually necessary unless more then two coats of color are applied. But then you soak 5 extra minutes/coat
2.) No white spots even if a light buffing (with a high grit buffer) is used.
3.) comes in 30 OPI colors.
4.) more durable. Clients can be more lax with their nails. (but not too lax)
5.) is LED or UV compatible.
6.) they will be releasing a MINX-like product compatible with the Gelcolor top coat.
Shellac frustrates me Bc:
1.) due to how different it is chemically then gel polish, you must be VERY meticulous in every aspect of Shellac. Each rule must be followed to the TEE to keep from compromising the service. NO BUFFING AT ALL (not even with the highest grit they make). This is the first cause of the white spots. They mean it when they say THIN LAYERS. This is the first reason it will chip! Shaking the bottle vigorously is the only way to keep from thickening. Thick polish leads to wasting product.
2.)Bc dsolve is not available here, I find that I have to apply solar oil after removal to keep my clients nails from drying completely out.
Gelcolor frustrates me Bc:
1.) if you have ANY extra layers, you must add 5 minutes to the already 15 minute soak time. This is fine unless you are doing creative things that I like to do
which sometimes can take an extra coat of something.
2.) you have to sell it to customers and explain y it is different then shellac but still a good product.
3.) there is not as much freedom for creativity. It's possible just more complicated (in my opinion)
I would use Gelish Bc:
1.) they offer a structure gel that soaks off easily
2.) it comes in the best colors for my girls who love what's new and in style. Like neons and pastels.
I don't use Gelish Bc:
1.) it requires breaking the top coat seal. Just an extra step I don't want to take. Filing also makes my clients very nervous Bc of bad experiences with NSS shops.
So that's MY personal take on three of the top products. As it's been already stated, weigh the pros n cons. But mostly... Listen to your clients!!
Shellac is my number one choice. Hands down. It separates me from everyone else.