there is no perfect, or best speaker for everyone.
this is like me telling you that my car is the best car in the world-- it is to me, but i doubt you have a similar opinion...
speakers are exactly the same-- every single one has different qualities, some are good, and some are bad. the trick is to locate the ones that fit your style.
1. use your own music-- the idea here is to be very familiar with what the music sounds like so you can hear what different speakers sound like.
2. try to demo all speakers using the same section of the track, and try to set all the sound settings on the test head unit to flat, or off-- so you are only hearing the qualities of the speaker, and not something the headunit is adding, or removing.
3. i like to start with the most expensive speakers they have--no matter how much more then my budget they are-- many times they will have better components, so the sound will usually be a little cleaner then others.
from there move down to your approximate budget, and then continuously switch back and forth between the speakers your considering to hear what they add or subtract from the sound.
some car audio dealers don't mind haggling the price, so don't be afraid to go slightly above your price limit for something that fits your needs better.
also, try to focus first on locating a speaker that fits your needs, and then from there work to your price range.
4.demo as many speakers as you can-- even if they are well below your price range, and/or the salesperson doesn't recommend them.
5. by this time, you should have spent a good time in the sound demo booth-- a good car audio shop should not have a problem with that, but might start to get impatient. poor shops just want to sell you something and get you back out the door..
i personally don't like being stuck to one brand for anything--specifically, speakers and subs can have dramatically different tones-- even from the same manufacturer. don't let the name on any product be the limiting factor-- you could end up missing out on the best speaker for you.
on my first car, i was up to about $1200 in car audio gear when i sold it--about $300 in speaker costs: a pair of 5-1/4 rev-series pioneer components, kenwood 5-1/4 coaxials, and a buy-one-get-one-free deal on kicker comps, and my current car is about the same in the way of costs, though the components have changed a little..
you don't mention amps, so i'll leave that out of the cost for now.. there is also the size, and amount-- 1-12" sub? 2-8's? there are many ways to do it.
the other option to try to save money if it comes down to it, is to build your own setup-- there are many guides to building crossovers, and companies like madisound.com, or parts-express.com sell a great number of individual speakers. if you first learn what you want out of a speaker, you should be able to use the reviews of the components that are available separately and build a setup that matches even the best car audio- specific component sets.. my component setup cost less then $150, but imo, does better then the $600 jl set i heard..