Number 1 competitor, no, because of the way they chose to go to market holds them down. Look how quickly Royal Purple has taken off, and think how Amsoil may have done if they did not choose multi-level marketing. Amsoil is the leader in technology and they were the first to bring synthetics to market (albeit badly), They developed 0W30 first, and has been copied by Mobil (reluctantly) through-out their existence. Mobil was happy to keep everyone at 3000 mile oil changes, regardless of what the auto mfgr recommends. As an example of how bad the Amsoil marketing teamis, they paid small fortune to sign Boyd Coddington as a spokesperson, about a month before he died.
As far as GM is concerned, I had the priveledge of attending a special Ecotech show in Englishtown NJ. GM paid for all Ecotech owners to display their cars, had a display of some of their latest prototypes. They gave us a tour of the pits, with about 4 Ecotech powered racers, up to 1500 HP. They gave us the VIP treatment. They took pictures of most of the cars, even commented about the wild 2 tone HHR, but were EXTREMELY careful to exclude my car, because of the Amsoil signs. I was even told by the GM Marketing manager ( nice guy) that they wouldn't show my car because of their Mobil 1 sponsorship, so yes, they do take it very seriously.
When Amsoil is questioned about the GM spec, their answer is that they did not submit a sample to GM for certification testing. I'd be willing to bet there is a price to pay for the testing and certification, call it waht you want, but it's kind of like a bribe to me.
As far RECOMMENDING oil, they are free to recommend a 0W30 while a manufacturer recommend 5W30, as it is a reecommendation, not an exact equivalent.

 

My experiance with Amsoil was in a Bug Eye Sprite. In race applications (H/Prod, SCCA) our car picked up 5 lbs of oil pressure at race temps on the track. Zero Rod and main bearing wear and failure all season. With dyno oil we changed bearings after each race as they were shot. Did not have too with Amsoil. We did not compair the other syn brands.

When I bought my Vette, it had dyno oil in it. On the first change I did I used the recomended Mobile 1 and lost 10 lbs of oil pressure in normal street driving and had very loud engine noise. I switched the Syntec and gained the pressue back and cut the noise.

Last week my local oil change shop had dropped Mobile one. For my second oil change on my SS and on my wifes PT Turbo, we changed to Castrol Edge. Although we don't have pressure gauges, both engines are noticably quieter. Looks like I'm going to stay with Castrol again.. Amsoil is to much of a pain to get when I want it. All our family cars (8) now run on Castrol edge.

 

My amsoil exp. came with racing dragbike. It was a 1075cc record holder Record is retired.. It ran 8.50's @ 151 or so. I always used Valvoline 10-30. I wanted to try something different, 2 weeks after change I blew a rod at 11,500rpm. Didnt connect it with oil. After that I had a brand new falicon crank in it with hardened rods... 2 months later that went too. Engine man said oil was probably a factor due to the markings on crank & rods... So switched back to valvoline. no probs after that till I stopped racing bikes in 06. May or may have been coincidence but who knows.

 

Amsoil usually uses higher viscosities for racing applications. However, the stresses of racing make choosing the right oil a "trial and error" situation, which can get kinda expensive, and like most products used for racing, no guarantee.

I started with Amsoil because I wanted their foam air filter for my 72 Buick. Great filter but did not take too kindly to backfires.

 

Make sure you use the correct filter. The kids jetta, turbo, requires mobile 1. Seeing that is a royle pain to change the filter, [by rights the belly pan should be removed, so i do it from the top looking down].. i tried the mobile 1 extended mileage filter which i never used before. shame on me..freaking piece of crap autozone stoned out kid gave me the wrong numbered filter..problem was, it tightened nice..didnt leak..my kid drove it away..she got 1/4 mile, oil had dumped out..engine quit..turbo engine ruined.

so, check your numbers, check the filters.