I don't quite understand the question, are you talking interior speakers? If so, then 6x8's or 5x7's are the usual answers. Most any manufacturer makes these sizes so listening to someone on here saying these are the best or that they sound great, means nothing if you don't like them. My suggestion is to go to a brick and morter specialty stereo shop, ask to see some 6x8 or 5x7 speakers, and do some comparisons.
Cause basically it is your ears that will be able to tell the difference. I run completely Focal in my car (their top of the line, but their 6x8s sound like turds) so your ears are the best decision makers you have. Good luck!
Joe