I've looked around fnfal.com and a few vendors, but I would like some first hand info on the current crop of rifles, kits, and receivers, without all the background noise over there.

Are there material or functional differences between Type I, II, and III recievers?

Which sellers have the best deals and least BS; i.e., what they sell matches what they advertise.

What do I avoid?

Are there material or functional differences between Type I, II, and III recievers?

There are no real functional differences between the receiver types for a semi-auto.   The changes were made for ease of manufacturing and high round full auto life span.

Which sellers have the best deals and least BS; i.e., what they sell matches what they advertise.

DSA ( www.dsarms.com ) is well thought of as a manufacturer.   They have both a completely new, made in U.S.A. rifle – the SA58 -- for around $1500.00 and a rifle made with like new Austrian surplus parts (Steyr), a new DSA receiver and the requisite number of U.S. parts for the rifle to legally use foreign magazines without switching out floorplates and followers – the STG58 -- for about $1000.00.
The best of the parts built guns, built by top-flight smiths like Derek at Arizona Expert Arms (www.azexarms.com) and Mark at ARS (www.arizonaresponsesystems.com ) are the equal to any FAL built anywhere, by anyone and between the top of the line DSA and the DSA parts gun in price.  Using some surplus parts is fine if they are of good quality, and some of the surplus parts on the market are brand new and made by manufacturers such as Steyr and FN.   Most of the best builders use either DSA receivers or Imbel – a FN licensed manufacturer in Brazil.

What do I avoid?

Century is hit or miss – mostly miss.   They do not have enough US parts to use foreign magazines legally and the US parts they use are of questionable quality.   Add in the abysmal workmanship of the assemblers and you get a rifle that may work, or may not, and if it doesn’t work you may be able to get it brought up to acceptable, then again you may not.

Avoid asking questions on AR-15.com that should be asked on the FALFiles?

Seriously, there is a wealth of info there, more than you can get here. You'll just have to sift out the "background" noise.

Well... Any Imbel receiver is likely to be very good (mine from FAC). My grade 3 kits (2) from Dan's Ammo/falparts.com had lots of finish wear but very little actual shooting wear. Cheap front stocks heat up real fast.

Maddock is right on with his answer. I had one of Arizona Response Systems FALs, they are absolutely first rate.  Mark's work speaks for itself.

The DSA kit guns are build with excellent (re:new) Steyr parts. When I got mine I couldn't tell the new from the used parts. The thing was flawless in apperance and performance.

There are only minor differences in reciever types, mine is a type II. The DSA web site does have a good explaination of the different types under their parts diagram - click on the receiver and you'll link to another page with the differences pointed out.

I went with the DSA as it uses an American receiver and enough parts not to have to worry about magazine parts counting. At the time both Arizona Expert and Arizona Response were shipping 6-8 weeks after ordering, DSA's were in stock - but that was a few years ago. I got my DSA for $795 plus shipping and tax, the Arizona rifles will be more than that but their custom made one-at-a-time.