Because there is no answer to your question. There is no "best." Plus you didn't give much info about your system goals. What do you want to accomplish, how much do you want to spend? There are ton's of great speakers out there, you'll just have to sift through to find the ones that meet your needs. Spend some time searching this forum and I promise a lot of your questions will get answered.
What kind of head unit do you have? Do you plan on going active, or do you want to stick with a passive component set? If passive, search this site for Boston Acoustics, Hertz, Focal, Premier 720prs. These are some of the more popular options. If you spend enough time reading threads about these, you will find plenty of other options. You may even decide you want to go active, which opens up a million more options.
It might help get responses if you posted amp specs too. The MC425 is 2x50 watts @ 4 ohms with a "little" head room. No need to spend mega bucks for components. There are plenty of DIY and pre-packaged drivers that will work just fine with 50 watts per channel and under your allowed budget.
THANX gijoe and macs
and yes i plan on going active
i plan on keeping the factory navagation head unit for right now until some time down the line.but i was wondering could i still get as good sound quality out of my factory head unit as a aftermarket for right now?