What it really sounds like you're getting at is that the beer you drink at a brewery is better than the beer you buy off the shelf at a store. I'd believe that. Beer from a brewery's tap is likely incredibly fresh, which most people would agree for most styles is better. Especially with how popular hoppy beers are in the San Diego scene, hops fade quickly...fresher will be way more aromatic. The beer you buy in the store may have been filtered or pasteurized, has been bottled and then sat in a warehouse for a while before being trucked around the county and then sitting on a shelf for a while before you hauled it back home.
However, is there an objective way to express "Fresher is better"? Dunno, probably not. You could run lab analysis and try to point at alpha and beta acid numbers, volatile organic oils or something...but it almost seems like trying to cobble together a theory after having made the conclusions already.
The BJCP was mentioned in another answer. What BJCP is, is an attempt to apply objective qualitative judgment to taste, which is inherently subjective, by asking folks to compare what they're sensing to an ideal example. Basically "How closely does this beer I'm tasting now adhere to description of the style of beer it's supposed to be?" They'll generally look at
- Head: color, density, how long it lasts.
- Aroma: malty? hoppy? spicy? grassy? sulphury?
- Visual: color, clarity
- Feel: thickness on the tongue, fizziness, acidity...
- Taste: malty, hoppy, spicy... balanced?
What you COULD theoretically do is drink the beer at the brewery, and then describe as if it was a BJCP description, then drink the beer from the store and grade it according to how close it resembles the brewery beer in those categories.
Outside of that, everything is subjective. What you feel like drinking, right now. The beer best suited to the weather will change with each season, beers best suited to the evening will change with what you're having for dinner. Hell, if you happen to be playing Skyrim maybe the beer with the dragon on the label will be better than anything else regardless what it tastes like.