you dont need to cut for those. stock holes allow for up to 6.5's.

As for the O.P.'s question.. my buddy just put clarion speakers into his prius and they sound okay. they lose quality very very quickly when u turn up the volume which is somewhat expected but not to the degree his get. personally.. i love Alpine but i've also heard good things about kenwood.

 

I have the best amps and subs JL audio makes.(jl w7s and jl 500/1 amps) The sound quality as well as how much abuse you can put them through is amazing. If you want the most amazing sound quality buy JL audio,but the **** aint cheap at all. If you want great sound quality but don't want to break the bank look at the alpine type S speakers and alpine head units(there new data recievers look nice) I personally run a pioneer premier, it wasn't too expensive and I love it. keep in mind the smaller the speakers the better they produce high pitch sounds,the bigger the speaker they produce better low pitch sounds. So if your looking to just get a simple upgrade to ur factory stuff get some nice mids like 6 or 6 1/2s

 

every sony xplode i ever had was trash,i would'nt go that route for sure....pioneer is real good..clarion is good to tho

 

eclipse or kenwood are my favorite head units. polk and infinity for tweets and mids and rockfords or infinity for subs.

i have installed lots of sony systems for people who liked them though. to brightly colored for me to put in my own vehicles though as i like to not have them attract attention of passer byers