Pioneer and infinty reference would be a good upgrade over stock.
I made my living in car audio for 20+ years. Sound is personal preference. Buy what sounds good to you. Try to listen to speakers you are interested in in someone elses vehicle, not on a sound board.
Honestly, new speakers will make your system sound marginally better, (going from 10 year old speakers to new ones), But it is really the head unit that will offer the most improvement. Changing the head unit will increase you frequency response by roughly 20%, not to mention giving you double, or in some cases, triple the power output.
When you do look for speakers, don't automatically by the top of the line, most expensive ones of any given brand. The higher end speakers are designed to work with outboard amplifiers, and are not as efficent as the models further down the line.
Bottom line: Anything will be an improvement over OEM.