The best place to buy a professional brand is through their distributor. Anywhere that sells a brand cheaper than the actual distributor might not be selling genuine products. I personally like Lilly Nails gel polish, my customers get 3+ weeks wear out of them and I like the colours. They have a base coat called structure base for anyone needing extra strenght. I have also heard many good things about The Gel bottle, but have not tried it myself. I have tried Shellac, but I am not as fond of it, I don't enjoy the colours as much (a subjective opinion) and I found they only lasted around 2 weeks, though the short removal time of shellac is good. When you find a brand you like, it's a good idea to invest in the whole system, since it's advised you have the correct lamp that goes with the brand you use, as well as the accompanying base and top coats etc. That way it's less likely for things to go wrong.
I agree. Why not stick with the brand you have until you get a bit more experience and then look at options? Once you know what you are looking for you can then trial different brands to find the one that ticks the boxes for you but always try and invest in quality. If you try and cut corners on prices it will reflect in quality and in return this could affect your reputation. If this is your business then invest into good products so that you can offer a reliable and safe treatment (and make sure you buy from a recognised UK brand to ensure that the products comply with legislation) x