Pot plants, just like any other plants, have specific nutrient needs. A fertilizer developed for roses isn't going to be optimal for tomatoes, even though it will work. While I believe much of AN's popularity is based off of hype and marketing, they are one of the only, readily available for me ( meaning i can go down the street and buy it NOW), pot specific nutrients, that contain more micro and macro nutrient in their base formulas than most other nutrient lines. I think there was one other, I believe dyna-gro, that was close but missing some other very minor trace elements. I was very,very hesitant to try the AN line, but after a few weeks of research, between both me and my partner, i figured it was worth a shot on one cycle.. I had a long convo with my grow shop guy and he even said the whole AN line is mostly crap, he said AN's base A&B, and a bloom booster and possibly a flavor enhancer - both from a different company. I had previously been using GH 3 part with ok results, but it is a "general" fert and i was using bloom/flavor boosters anyway.
I don't believe any of the "countless proven" threads about nutes, after looking at literally hundreds over the last month I've only seen a handful that had controlled as many variables as possible and even then there were still variables ( mostly environmental) that could have contributed to the differences in growth/yield between nute line ups. The few i saw that actually look fairly well controlled and unbiased did show a slight, SLIGHT, advantage to the AN BASE lineup, I guess only trial and error will tell if it's worth the extra money to you. Honestly if I don't see a significant difference between AN and GH I'll go back, not worth 2-3x the cost if the results aren't there.