Well everyone has a different opinion, so here is mine.
Clarion is a very good quality head unit with a great sound - the only downside is its low wattage output 14 x 4 (average) compared to Pioneer's 35 x 4 (average). In my opinion though, the 14 is more than enough and can be heard a pretty good distance away. The more wattage you play with, the greater the chance that in the future you will be saying frequently "excuse me, what did you say... can you speak up."
I am running 6 x 8s on all four doors, but recently I was discouraged at the explorer's horrible "front staging." The speakers are aimed at each other and once someone is sitting in the seat chances are that their leg is blocking the sound a bit. I solved this by purchasing a set of Rockford Fostgage Fanatic tweeters (angled type and can be moved around). I made cut outs on the top of the door where it is still flat (triangle shaped). The sound is a 100% improvement. The type of speakers can make a difference (component sets); however, the real difference is where the speakers are positioned. {PIONEER 6x8 TWO WAYS}
I am running Rockford Fostage 12" subs and provide a very nice rockin to the truck. They are tucked inside of a sealed Q-Logic box. You can go with 15"s if you want your bass felt ten cars back and to register on the richtor scale, but you will need lots of power. You can also try the box in the back cutout area (I have a Kicker Solo-Baric 10"); however, one woofer probably won't satisfy your hunger for serious bass. Good woofer brands are easy to come by RF, Kicker, Cerwin Vega, MTX just to name a few. It all depends what you want - If you want loud sound you could even try a kicker factory box with 2 - 12" woofers and two midranges (ported) - bass and sound.
Everyone will give you different opinions and the are all good. What you have to use is the amps RMS rated power per channel. If you run a 2ohm load, the power rating goes up. Also you should look for an amp that has a bass boost for your woofers. Don't go with a cheap amp - it will be your worst nightmare (cracking when bass hits hard and bass won't even hit that hard.) From my experiences Sherwoods are good for starters and those who have an average budget. I am currently running Crunch amps, but will be running two amps so I am switching to Rockford Fostages - very good.
This is all the time I have.
