Learn Hardcore Finnish: Valitsen mieluummin luontoretken kuin ostosmatkan. - I would rather choose a nature trip than a shopping trip.

Valitsen is the first-person singular present tense form of the verb valita (to choose). You form it by taking the stem valit-, adding the present-tense marker -se-, and then the personal ending -n:
valita → valit- + se + n = valitsen (“I choose”).

What is the function of mieluummin, and how is it formed?

Mieluummin means “rather” or “preferably.” It’s the comparative adverb of mielellään (gladly). You form it by replacing -ään in mielellään with the comparative suffix -ummin:
mielellään → mieluummin (“rather/gladly rather”).
In sentences it’s used in structures like mieluummin A kuin B (“rather A than B”).

Why are both luontoretken and ostosmatkan in the genitive case ending in -n?

The verb valita takes a total object in the accusative, which in Finnish can appear as either nominative or genitive singular. Here both luontoretken and ostosmatkan are in the genitive singular (the “-n” ending) to mark them as definite, total objects. In comparisons introduced by kuin the second term must carry the same case ending as the first for symmetry.

What is the role of kuin in this sentence?

Kuin is the conjunction used for comparisons—equivalent to English than. In the pattern mieluummin A kuin B, kuin links the preferred option A with the less preferred B.

Could I use the nominative singular (luontoretki, ostosmatka) instead of the genitive here?

No. With valita you need a total (definite) object, which in Finnish is expressed by the genitive singular -n ending. The nominative singular would be ungrammatical in this context.

How do compound nouns like luontoretki work, and how are they declined?

Compound nouns in Finnish are built by joining two (or more) stems, here luonto (nature) + retki (trip) = luontoretki. The entire compound follows the declension pattern of its second component (retki, which is a type 2 noun):
nominative sg – luontoretki
genitive sg – luontoretken
inessive sg – luontoretkellä, etc.

Can mieluummin appear in different positions in the sentence?

Yes. Finnish has flexible word order. You could say:

Mieluummin valitsen luontoretken kuin ostosmatkan.
Valitsen luontoretken mieluummin kuin ostosmatkan.
Valitsen mieluummin kuin ostosmatkan luontoretken.
Each variation shifts the emphasis slightly, but the core meaning “I prefer a nature trip to a shopping trip” stays the same.

Are there other ways to express “rather than” in Finnish besides mieluummin … kuin?

You can also use comparative adverbs like enemmän (“more”) in a structure such as valitsen enemmän luontoretkiä kuin ostosmatkoja (“I choose nature trips more than shopping trips”), but that focuses on frequency or quantity rather than preference. For direct preference, mieluummin … kuin … is the most natural equivalent to “rather … than ….”