Ok, everyone knows that running aluminum diff cups (inner diff housings) increases drive-train strength and durability, but deciding which ones to run is a little tricky with all of the options that are available. Well, since I am building new diffs for my project Revo, I decided to get a set...and while looking at all of the cups available, I noticed a few differences that make or break each one.
As we all know, aluminum does not make a very good wear surface, so it is not a good idea to have a harder material (such as steel) constantly rubbing against it, because the harder material will quickly wear away the softer material...which causes lots of slop, and will eventually lead to catastrophic failure. During my search for aluminum diff cups, I came across some bad ones, some good ones, and some extremely good ones...here is what I found.
I will start with the worst ones and work my way to the best ones, rating them 1 through 10 (10 being the best)...
 This is the Golden Horizons aluminum diff-cup; It is made of billet 6061 aluminum, and has the steel output shaft riding directly against the aluminum cup. To make it even worse, the ring-gear mounting holes go all the way through the cup, making it more likely to leak diff oil.
 This is the RD Logics aluminum diff-cup; It is also made of billet 6061 aluminum, and also has the steel output shaft riding directly against the aluminum cup. It's not as bad as the GH cup, but it's still pretty bad.
 This is the Team Integy aluminum diff-cup; It is made out of cast 7075 aluminum, which is a lot harder and more durable than 6061, but the steel output shaft is much harder than even 7075 aluminum, and the cup will still wear out very quickly. Cast aluminum is junk, even if it's 7075 cast aluminum.
 This is the Nova RC Products aluminum diff-cup; It is made out of billet 7075 aluminum, but like the Integy cup, it has the steel output shaft riding directly against the aluminum cup. Billet 7075 aluminum is the best aluminum you can buy, but it still can't hold up to steel constantly rubbing against it.
 This is the RC BEST aluminum diff-cup; It is made out of billet 7075 aluminum, and has a billet brass insert for the steel output shaft to ride against. Brass is a very hard material, much harder than even 7075 aluminum, and has excellent wear properties that are very similar to steel...and it even has a very good lubrication quality, that allows the steel output shaft to ride against it with almost no friction at all. This is a very good design, but not quite the best.
 This is the Hot Racing aluminum diff-cup; It is a 2-piece design, and is made out of billet 6061 aluminum and G-410 stainless-steel! The main cup is made out of lightweight 6061 aluminum, but the outdrive plate where the steel output shaft rides is made out of ultra-hard (but still lightweight) G-410 stainless-steel. The 6061 aluminum and G-410 SS 2-piece cup is the same weight as a 1-piece cup made out of 7075 aluminum, so weight is not an issue. This is the ultimate diff-cup, with virtually no wear at all! This, my friends, is a perfect 10...and is what I am going to run in my BL Revo!