Since no one else has chimed in, let me say this.
WEIGHT:I have a Champro mag (old style) and the weight on both the AS and Champro models are similar. Both are under a pound and wicked light. This is a tie.
LOOKS: I like the looks of the new model Rampage Mag (Champro), but not as much as I like the AS Mag. Champro is more Japanese-styled, while the AS is just very cool and rugged. I think the AS Mag is more popular due to it's neat looks and high visibility (read as seen on MLB umpires). I'll give this round to AS.
FINISH: Finish on the Champro fades really fast I've heard - but I've seen AS masks also fade pretty quickly. I'd say this is a tie.
DESIRABILITY: In my humble opinion, there's a brand snobbishness here somewhat. Folks don't mind AS at all, but some don't want to say they're wearing a Champro. Unfortunately, like Smitty used to mean a bad umpire - Champro generally means not as good quality/cheaper. This is a shame because they make some excellent products (sun visors, brushes, indicators, Mag mask, etc.). AS gets the nod here.
VIEW: I can't fully speak to this, so I'm going on what I've heard from Champro Mag owners. With TW pads, the view on the Champro is quite good. The AS Mag is also the same profile; however it has large flat blades which take some getting used to for the bars. Once you adjust it, it will also offer a really good view. IMHO, the Champro opens up just a bit more vision than the thin AS Mag eye port. If I'm being unbiased, I'd say either a tie or maybe even leaning a bit towards the Champro here.
SAFETY: The AS Mag is tested by All Star as pointed out already. Plus, it has a ton of angles built into the mask to help deflect a baseball. Finally, it has new pads with a plate inserted into the jaw pad for safety. The Champro also has lots of angles and is designed to help deflect baseballs, but their pads are junk and harness is a joke. AS gets the nod here. (Note: I do recommend the con-cushion mask pad from Gerry Davis if you wear either mask as they are both wicked light.)
PRICE: Now on the most obvious difference of them all - price! I've seen the Champro models on sale for $80 shipped (eBay, Sideline Swap, etc.) on a new mask. Of course, then you have to buy new pads and a harness ($55-60 investment with shipping). So, let's say a functioning price for the Champro Mag would be $140-150. While the AS Mag will sell for $225 about anywhere. The Champro definitely wins this round.
REPLACEMENT PAD COST: The Champro should use most regular pads from what I have heard, although I hear that most are using TW in these. I have heard Wilson wrap-arounds will not work in the Champro because the mask bars are too thick. So, let's say $40 on TW or regular Wilson pads. AS Mag pads are $45, but some choose to use TW or other pads in the AS Mag too, so cost is about the same here. The AS pads are also safer, thanks to a plate infused into the lower jaw pad to help spread out contact. This is a tie.
FINAL SCORE: AS: 3 nods, Champro: 2 nods, with 2 ties.
SUMMARY: In summation, they are both very good masks. With the Champro, you have to do a bit of work to get the pads and harness you like, but that can be fun. We all love to create our own look or mirror the look of an umpire we admire. The AS is the Lexus if you will, while Champro may be the Hyundai or Toyota. Both will get the job done. One is about $75 less than the other. In the end, like so many other times - get what you like and try them on, see how you like the fit and view. Do you feel safe? Go with what pleases you more. You only have one brain though, so protect it at any cost!
(Full disclosure: I have a new old-stock Champro Mag model with the head extension and square chin-guard and I have a black matte AS Mag. I like them both and wear them both.)