Ystäväni haluaa aina ikkunapaikan, mutta minä valitsen mieluummin käytäväpaikan.

-ni is a possessive suffix meaning my.

• ystävä = friend
• ystäväni = my friend

Finnish often adds possession directly to the noun instead of using a separate word like my.

A useful extra note: ystäväni can sometimes also mean my friends, but here the verb haluaa is singular, so in this sentence it clearly means my friend.

They are the objects of the verbs haluaa and valitsen, and here Finnish uses the singular total object form.

• base form: ikkunapaikka = window seat
• sentence form: ikkunapaikan
• base form: käytäväpaikka = aisle seat
• sentence form: käytäväpaikan

In many grammar explanations, this is described as the total object, and in the singular it often looks the same as the genitive, with -n.

Why this form here? Because the speaker is talking about choosing or wanting one whole seat as a complete item.

Compare:

• Haluan ikkunapaikan. = I want a/the window seat.
• En halua ikkunapaikkaa. = I do not want a/the window seat.

Notice how negation usually changes the object to the partitive: ikkunapaikkaa.

mieluummin means rather, preferably, or more willingly.

So:

• valitsen mieluummin käytäväpaikan = I would rather choose an aisle seat
• more natural English: I prefer an aisle seat

It is used when comparing one option with another. In this sentence, the other option is the window seat, mentioned earlier.

Yes, Finnish could absolutely say mutta valitsen mieluummin käytäväpaikan.

Finnish often leaves out subject pronouns because the verb ending already shows the person:

• valitsen = I choose

So why include minä here? For contrast and emphasis:

• Ystäväni haluaa... mutta minä valitsen...
• My friend wants..., but I choose...

It highlights the difference between the friend’s preference and the speaker’s preference.

Because Finnish usually writes compound nouns as one word.

• ikkuna = window
• paikka = place/seat
• ikkunapaikka = window seat

And:

• käytävä = aisle
• paikka = place/seat
• käytäväpaikka = aisle seat

This is very normal in Finnish. English often writes similar ideas as two words, but Finnish usually combines them.

The dictionary forms are:

• haluta = to want
• valita = to choose

In the sentence:

• haluaa = he/she wants
• valitsen = I choose

A quick comparison:

• minä haluan = I want

• hän haluaa = he/she wants

• minä valitsen = I choose
• hän valitsee = he/she chooses

So valita does not become valitan in the first person. Its present-tense stem is valitse-, giving forms like valitsen and valitsee.

Finnish has no articles, so there is no direct equivalent of English a/an or the.

That means:

• ikkunapaikan can mean a window seat or the window seat
• käytäväpaikan can mean an aisle seat or the aisle seat

The exact meaning depends on context. In this sentence, English most naturally uses a window seat and an aisle seat, because it is talking about preferences in general.

Yes. This is one of those forms that can be ambiguous on its own.

• ystäväni can mean my friend
• ystäväni can also mean my friends

But the verb usually makes it clear:

• Ystäväni haluaa = My friend wants
  because haluaa is singular

• Ystäväni haluavat = My friends want
  because haluavat is plural

So in this sentence, there is no real confusion.

aina means always, and its placement here is very natural Finnish:

• Ystäväni haluaa aina ikkunapaikan.

A common neutral word order is:

subject + verb + adverb + object

So here:

• Ystäväni = subject
• haluaa = verb
• aina = adverb
• ikkunapaikan = object

Finnish word order is more flexible than English word order, so other orders are possible for emphasis, but this version sounds normal and straightforward.

Yes. mutta is the standard Finnish word for but.

In this sentence it connects two contrasting ideas:

• Ystäväni haluaa aina ikkunapaikan
• mutta minä valitsen mieluummin käytäväpaikan

So the meaning is:

• My friend always wants a window seat, but I prefer an aisle seat.

It is the most natural basic conjunction here.