You are so right! There are dozens of excellent brands out there and it can be confusing to choose. Shellac, Gelish and Cuccio are great brands, but I'd add OPI, LeChat, and IBD to your list for consideration; I'm sure others could add more. In your case where you already have an established business and clients, I would start with what you already have. Do you already use a brand that you are happy with? Do you have a relationship with a vendor or supplier? Have your clients expressed an interest in a brand? Do you want the pull of a major brand like Shellac, OPI, or Gelish or are you comfortable with a lesser known brand? What about marketing, customer support and training? It's hard to beat CND or OPI for that. Do you want associated products like scrubs and soaks and creams? Do you need a product that is hypoallergenic? Do you want to only have one gel polish brand?
There's no one correct choice or best polish for everyone. It depends on your clients' and your business' needs. I've worked with dozens of brands and it just got crazy with all the lamps, and base coats, and stuff, so I have narrowed mine down to OPI, LeChat,and Cuccio. But I still think very highly of Shellac (hypoallergenic) and IBD (great price point) and Artistic Colour Gloss (amazing colors). I did not like Orly or Gel II (difficult removals), Essie (streaky, inconsistent color), or Gelish (poor quality control on color and formula).