Any brand will be ok so long as you spend about £50 plus. I'd recomend Pioneer, Alpine or MB Quart for front speakers.
Components will give you a much better sound, but you need to mount the tweeter as high as possible to get the most benefit (top of door card, A-pillar or dash)
The MB Quart speakers are a gem but cost a fortune. For some good prices on speakers check out
www.caraudiosecurity.com or
www.bassjunkies.com.
Also, spending £15 on a dynamat doorkit will help improve the sound quality of any speakers.