One of the hardest questions to answer is which brand should you choose.
There are hundreds of brands on the market, each catering for a specific need and price bracket. Unfortunately there are not a great many resources providing feedback regarding tried and tested equipment. Every equipment producer will always promote their product with a bias towards making a sale (which is only natural), however your aim is to purchase equipment which fits your requirements exactly. I would recommend watching a few similar performers at different sized venues and listening to the quality of sound.
Don't be afraid to approach the artistes with a few questions, as many people are only too willing to provide honest feedback on equipment they are currently using, and equipment they have previously purchased, but now avoid. These are the best people to provide advice as they are not trying to sell the equipment, and have also had the opportunity to put the equipment through it's paces.
Some typical well-established brands are:
Mackie, EV (Electro-Voice), RCF (purchased by Mackie in the mid-90's), Crown, Nexo, Dynacord, QSC, Crest, Roland, JBL, Boss, Alesis, Tascam (Teac Professional Division), Studiomaster, Peavey, Sennheiser, Shure, Lexicon, Soundtech, Beyerdynamic, Chevin, Cerwin-Vega, AKG, Audio-Technica, Soundcraft, Yamaha, Beyerdynamic, Bose, DAS, Allen & Heath and Marshall.
Although there are hundreds of brands to choose from, it is important to remember that although a product may carry a brand name, there are always low-budget pieces of equipment produced by these companies, which may not perform as good as the mid to higher range of equipment, but may be an ideal starting point depending on your available budget.