No quiero esa, prefiero la anterior.

Esa means that one / that [feminine noun]. It is a feminine singular demonstrative, so it agrees with an implied feminine noun such as camisa, opción, falda, mesa, etc.

So:

• esa = that one for a feminine noun
• masculine equivalent: ese
• plural: esas / esos

In this sentence, the noun is not repeated because Spanish often leaves it understood from context.

There is an implied feminine singular noun that both expressions refer to.

For example, the full sentence could be something like:

• No quiero esa camisa, prefiero la camisa anterior.
• No quiero esa opción, prefiero la opción anterior.

Spanish very often leaves out the repeated noun when it is obvious. English does the same with that one and the previous one.

Because anterior is being used like a noun phrase: the previous one.

Normally, anterior is an adjective:

• la página anterior = the previous page

But when the noun is omitted, Spanish usually keeps the article:

• la anterior = the previous one

So the article la is necessary here because it stands in for the missing feminine noun.

Spanish often drops subject pronouns when the verb form already shows who the subject is.

• quiero = I want
• prefiero = I prefer

Because those forms clearly indicate yo, Spanish normally leaves yo out unless you want emphasis or contrast.

For example:

• Yo prefiero la anterior, no tú. = I prefer the previous one, not you.

In a neutral sentence, omitting yo is the most natural choice.

Both verbs are stem-changing verbs in the present tense.

• querer changes e → ie:
  quiero, quieres, quiere...
• preferir also changes e → ie:
  prefiero, prefieres, prefiere...

So:

• No quiero = I don’t want
• prefiero = I prefer

This change happens in stressed syllables in the present tense for these verbs.

Both are possible, but they do slightly different jobs.

• No quiero esa = I don’t want that one
• No la quiero = I don’t want it

Esa points out or identifies the item more explicitly: that one.
La is just a direct object pronoun: it.

If you are choosing between visible options, esa is very natural because it contrasts one item with another.

Here anterior means previous, earlier, or the one before.

So la anterior means:

• the previous one
• the earlier one
• the one before that

It does not usually mean in front here. In this kind of sentence, it refers to sequence or order, not physical position.

Yes, but the meaning changes.

• prefiero esa = I prefer that one
• prefiero la anterior = I prefer the previous one

So esa points to a specific item as that one, while la anterior identifies it by its position in a sequence.

Because they must agree with the implied noun, which is feminine and singular.

Examples:

• esa camisa / la anterior
• esa opción / la anterior

If the hidden noun were masculine, you would use:

• No quiero ese, prefiero el anterior.

Agreement is very important in Spanish, even when the noun itself is omitted.

Under current standard spelling, it is normally written without an accent: esa.

Older spelling sometimes used accents on demonstrative pronouns:

• éste, ésa, aquél

But modern standard Spanish generally writes them without accents unless there is a real ambiguity, and even then the accent is usually avoided.

So esa is the normal modern spelling.

The comma links two short, closely related clauses:

• No quiero esa
• prefiero la anterior

This is natural in Spanish when the second clause explains or contrasts with the first.

You could also say:

• No quiero esa; prefiero la anterior.
• No quiero esa. Prefiero la anterior.

All are understandable, but the comma gives a smooth, conversational flow.

It depends on the tone.

• No quiero esa, prefiero la anterior. = smooth and natural
• No quiero esa, pero prefiero la anterior. = usually not ideal, because but is not really needed
• No quiero esa; prefiero la anterior. = slightly more separated

Since the second part naturally contrasts with the first, Spanish often leaves out pero.

A more natural use of pero would be something like:

• No quiero esa, pero tampoco quiero la anterior.

There, pero adds a clearer contrast.

Sometimes, but not always with exactly the same feel.

• la anterior = the standard, very common way to say the previous one
• la previa can work in some contexts, but it is less universal and often sounds more formal or more tied to certain nouns
• la de antes = the one from before / the earlier one, more colloquial and very common in speech

So in this sentence, la anterior is the safest and most standard choice.

You would change the demonstrative and the article to match the noun.

Masculine singular

• No quiero ese, prefiero el anterior.

Feminine plural

• No quiero esas, prefiero las anteriores.

Masculine plural

• No quiero esos, prefiero los anteriores.

The pattern stays the same; only agreement changes.

Yes, it is completely natural in Spain Spanish.

It sounds like something you might say when choosing between items:

• clothes
• menu options
• pages
• photos
• versions of something

A native speaker in Spain would understand it immediately as I don’t want that one; I prefer the previous one.