One thing to note, is that car speakers pretty much operate at 4ohms. They will be louder, but make sure your amp can deal with that level of ohm resistance. It can permanently damage the amp over time, if not suited for it. (many amps have a toggle switch to change ohm setting)
You can also wire speakers up in serial or parallel, to change the Ohm resistance. Search for it, and you will easily find the details to do so.
The worst thing is... if you use a standard on-board sound... You just wont get the quality of sound found on a simple ancient soundblaster audigy.. nor even cards before that model. Onboard is horrible. Even the best speakers, wont change it.
Probably 99% of PC speakers are a rip total off. You can find better quality, at cheaper prices, in other forms. Many cheaper model woofers smaller than 6" dont have very good bass. Trying to use a tiny cheap woofer + powered subwoofer, isnt the same as a good quality woofer alone. Subwoofers dont handle things like the punchy upper bass range, and so your missing a lot of detail as a result.
Also, ported speakers, are well inferior to 'sealed-air' speakers. Tuned 'port holes' create an ugly artificial bass sound. The middle ground is use of a passive radiator... but even that can be inaccurate.
A good tweeter, with a good sound signal.. can produce sounds so real, you can be fooled thinking someone is behind you, its raining outside..etc. They have a 3d soundstage, so you actually hear as if you are in the middle of a real concert / event. You can actually get a feel for how far things are away from you... and even behind you. Its really amazing. One such tweeter came from EPI's time and energy series... called an 'inverted tweeter'. (not a typical dome) Ive also heard similar things from ribbon tweeters too.
A good EQ can help bring a not so perfect speaker, to life. Most good soundcards have at least a treble and bass tweak. Additional tweaks cab be done with plugins if needed... or by the amp itself, or with an actual physical EQ.
If you want to Feel the bass, but not wake the dead... nor blow out the windows... Get a set of
tactile transducers. (like the Aura Bass Shakers at Parts Express or ebay) They create very strong vibrations at very low wattage, with very little audible sound. On max setting, with 2 of them under my pc chair, there was so much vibration, that my eyes couldnt make out what was on my static pc screen.
Some speakers are much louder than others (lower watts, could blow them easily if not careful)... but the expense is in accurate quality. A lot of loss and distortions of the original signal. When you hear crystal audiophile grade sound, you never can go back. You dont miss the higher volume levels, as the sound is so much more satisfying, even at mild levels.
Vintage speakers can turn out to be some of the best, if your lucky to score them. But know that you probably will have to get them re-foamed at minimal, and capacitors may need replacement, as they get out of whack with age.
Many ported speakers wont sound right if they are de-cased. They are set up for a certain air volume, and also need the tuned port hole, for their low-end.