I use TGB's BIAB (Builder in a Bottle), which I love, so to make it worthwhile buying their lamp to ensure a proper cure I decided to buy some of their gel polishes too. I have to say they are lovely to use and have a huge choice of colours and gorgeous glitter polishes to choose from. They last really well too (but you do need to follow their application guidelines thoroughly as they're different from most other brands).
I personally think they are too expensive, despite the bigger bottles and I only buy them when they have a sale on - which in fairness is quite regularly. (They've currently got 25% off and had 20% the other day for a while too!). They do run out of popular products quite regularly though - including the lamp, which is a shame as they are attracting new clients every day and I think they should be able to provide the correct lamp at all times. Delivery times are usually very good, but when they have a big sale on they can often take up to 10 working days to arrive.
I have only used Magpie glitters so can't comment on their gel polish.
Another brand well worth looking at is INK London. The company produce their own products and only sell direct to the client so can keep their costs down that way. They have a fantastic support team and also offer lots of training courses (TGB do now too)
INK and TGB are my favourite brands.