That really depends on your current setup IMHO, I mean are you going to add an amp and possibly a sub as well in the future, or do you just want a louder and clearer sound?
The Sony's are good for the price, just keep in mind that you do get what you pay for. They're speakers are made in china and aren't of the best quality and they do sound better then your stock speakers provided you drive them with an aftermarket head unit, stock head units just dont have the power to push an aftermarket speaker and will make any choice sound muddy, and will damage the speaker in time.
The Infinity's sound great up high, really full and crisp but lack a bottom end on them. They'd sound best if you amped them as well as used a sub in your car in tandem with them.
The Alpine type-S line of speakers have more of a kick down low, and would also work alot better amped as well, they are what I would reccomend if you were going to amp your system.
Whatever you get go for a component system over standard coaxial speakers, component meaning the tweeter and midwoofer are seperate and come with a crossover, versus coaxial speakers where its all in one package.
If you really need help with car audio check out
www.the12volt.com and read read read...
Andrew