Big Is Not Always Better:
Big speakers don't necessarily play louder or sound 'bigger' than small ones, nor do they necessarily have better quality bass. Your system can be split approximately into two halves (50% of quality comes from the speakers, the other 50% comes from the amplifier/mixer/microphone and effects). One doesn't perform to it's potential without the other. All speakers require a compatible amplifier. If the amplifier cannot produce enough power to drive the speakers correctly, the speakers are unlikely to sound as good as intended. An amplifier that outputs too much power for the speakers is likely to introduce distortion to the sound.
The general rule of thumb is to think about the size of venues where your equipment will be used, decide on your budget and then purchase compatible speakers and amplifiers. Although many manufacturers produce matching speaker/amplifier packages, you can mix and match with different brands as long as the outputs of the equipment are compatible.
Product Worth A Mention:
Although we appreciate that artists will always have a preference, every once in a while a product is produced which stands the test of time regarding performance and durability. One of the products we feel we must give a mention to is the Shure SM58 microphone. Still used by seasoned pro's today, if you want a durable first microphone at a price that will not break the bank, you can't go far wrong using one of these. Over a number of years the SM58 became the vocal industry standard for consistent performance and durability that very few other microphones have been able to emulate. Please purchase from an equipment retailer, as there have been many inferior quality counterfeits manufactured which do look quite convincing.