»Aufs« is a short form for »auf das« (like »don't« is a short form for »do not«), and »das« is an article for neuter nouns:
Der Rauchfangkehrer steigt auf das Dach.
Der Rauchfangkehrer steigt aufs Dach.
The chimney sweeper climbs onto the roof.
Der Bauer geht hinaus auf das Feld.
Der Bauer geht hinaus aufs Feld.
The farmer goes out to the field.
This works because Dach and Feld are neuter nouns. It does not word with male or female nouns, because they do not have the neuter article »das«:
Der Wirt stellt den Krug auf den Tisch. (»Tisch« is a male word)
(There is no standard German short form for »auf den«.)
The host puts the jug onto the table.
Der Bauer geht hinaus auf die Wiese. (»Wiese« is a female word)
(There is no short form for »auf die«.)
The farmer goes out to the grassland.
But instead of normal nouns you also can use a special class of nouns, which are called »substantivierte Adjektive« (nominalized adjectives). Those words are NOT Adjectives! They are nouns, but they derive from adjectives. And because they are nouns, you have to write them with an uppercase first letter in German! And because they are nouns, they also can be used with an article. (In fact an article before a word that looks like an adjective is a very heavy hint for this word to be an nominalized adjective, i.e. a noun.)
You have nominalized adjectives in English too, but because you don't write nouns with uppercase first letter, you don't need to take care of it very much.
Here is an example:
The poor and the rich.
Here poor and rich are nouns. You can see it, because they do not describe an other word like every adjective does (like in »the poor man«, where poor is an attribute of man), and because both words have an article. (In »the poor man« it is the word man that has the article; not poor!)
In German there is a construction, where you take the superlative of an adjective, transform it into a noun, and then put »auf das« or »aufs« before this word, to use the hole thing like an adverb:
- Positiv: gut (good)
- Komparativ: besser (better)
- Superlativ: am besten (best)
Make a noun of the superlative: der/die/das Beste (the best) (german nouns are always capitalized! So it has to be »das Beste«, not »
Put »auf« (to) before it: auf das Beste = aufs Beste (to the best)
Now use this group of words like an adverb:
Markus erledigt seine Arbeit aufs Beste.
Markus does his job to the best.
Of course, you could also use a real adverb:
Markus erledigt seine Arbeit bestens.
Markus does his job best.
Or you might also use the normal superlative:
Markus erledigt seine Arbeit am besten.
Markus does his job best.
capitalization of nouns
Keep in mind, that nouns in German are ALWAYS capitalized! There is no exception of this rule! So, when you say:
An alternative to am schnellsten, am besten, etc. is the use of aufs schnellste, auf beste, etc.
Then I have to answer, that this is wrong. This is correct (and don't forget the s at the end of aufs):
An alternative to »am schnellsten«, »am besten«, etc. is the use of »aufs Schnellste«, »aufs Beste«, etc.