With regards to glasspacks, almost all brands use this technology (except flowmaster. Allied is actually known as a resonator but it is a very good quality glasspack similar in design to the styles from the 60's and very resonably priced (around $30). Tae a trip to a good muffler shop, drop the muffler, start the engine and check out the sound, then have them hold up differernt mufflers to see which one gives you the sound you like best.

With regards to performance, check out broaderperformance.com for their muffler flow test...guess what, Flowmaster isn't the best and glasspacks are not as bad as what many think.

 

i have an 04 v6 with a flowmaster 50 SI/SO dumped. it sounds good to me, great exhaust note and has a great idle sound. doesnt sound anything near ricey, i absolutely love it. im thinking about changing to a SI/DO and getting duals out the back, getting tired of the turn down. anyway, follow these links and take a listen to my truck exhaust.
http://www.youtube.com/watch?v=bciVcUo3fqo
http://www.youtube.com/watch?v=J0722S5LCsw

 

I have a true dual setup with flowtech redhots 2.5" glasspacks on my 05 and they sound crazy loud. If there was word more Extreme than Extreme I would use it to describe the low rpm sounds in the 0-30mph mark. WOT is loud as hell too but my packs don't exit and are underneath the truck so the interior resonance is equally loud making long trips not so enjoyable especially for the passenger Wife likes it but doesn't want it on her 5.4 of course I do! Only thing is the back pressure is pretty interesting around 70mph and above so a lot of popping goes on letting of the gas but that's easily fixed. I had the same setup on my 97 4.2 when I had her and the 05 is just louder, I think Ford took of a couple of pre-cats in the newer models. If you want just want it loud get glasspacks I gurantee them after installing two setups. Get 2.5" only though.

 

Not much to look at since it's only a straight pipe. But here is the Heartthrob.