How to say "which one" in Russian (feminine - example: for dresses "Which one should i buy?")
Какое and которое are quite similar in meaning, but the latter is not an open-ended question, it assumes a choice out of several possibilities.
- Какое платье мне купить? // What dress should I buy?
A valid answer might be "a long one", "a red one" or "this one".
- Которое платье мне купить? // Which dress should I buy?
This question assumes the buyer has several dresses to choose from and needs to pick one.
Well, a dress as платье is indeed not a Feminine but a Neutrum word, because it ends in -е (like the rest of -е, -о and -у-ending Neutrum words).
But then, we have одежда, which is less gender-specific socioculturally but is a Feminine word indeed.
If you want to practice some mental acrobatics with Gander/Case/Definite-Indefinite/Animate-Inanimate criteria, you should observe the options for each pair in each case (depending on Animate-Inanimate opposition, an object in Masculine gender could be either in Genitive-like or in Accusative form):
Masculine: какой/который (Inanimate) или какого/которого (Animate)
Neutrum: какое / которое
Feminine: какую / которую
This refers to the objects cases only.
An easier and universal construction (which could sound to a native speaker a little bit strange due to its modality of being non-evident/indefinite) is Что за...?.
It goes like this:
Что за платье / куклу вуду/ сотрудника / компьютер тебе взять?
In the given question "Which one should i buy?" I would separately focus on two words, "one" and "should".
The answers given suggest the full phrase "Which of the dresses ...". However in casual speech repeating the topic every now and then often feels excessive, that is why "one" is used instead of "dress".
Depending on the informality level, upon how close are relations and how recent was last mentioning of the topic (like, if you were to the shop month ago - no one would understand which "one" was meant. OTOH going out of the dressing room holding a pack of dresses makes the topic obvious), there can be few options more or less verbose.
Какое из них купить? - Which [one] of them to buy? Какое покупаем? - Which [one] are we buying? Ну и какое?/Ну и которое? - So [in the end] which one?
They are very close, so hard to draw the line. For me the "который" pronoun has a slightly different shade, as I feel it. It hints that there is some pressing need, some task to do with one dress, but you do not know which one. Like "Did you washed that your dress clean?" "Which one?" - "Ты отстирала своё платье?" "Какое именно?"/"Которое?" Or like leaving a dress-room with a pack and met with "Still i think the dress bears an unreasonable pricetag..." you can demand clearance "Which one" - "Которое?". There is a fixed and readily available list of thing, and you have to point into it. Like Quassnoi's comment with "которое из двух" - there is an immediate list of two options, stop hesitating and put your finger upon one of the rows!
But personally in a general surfing around the shop and looking here and there, and maybe deciding to buy nothing or buy pants instead of dress - in such a blurry situation "кoторое" would feel a bit unnatural, a bit too specific, a bit too focused, demanding. Again, in such a surf-around there is not fixed and specific list to point your finger. There is some general idea of dresses suiting better or worse. So, "какое" would feel more natural for it.
The "shall" verb, as I heard, is a very demanding one. To the point in British English today even I/We is often used with "will" instead.
So, i'd start with softer options.
"Какое платье мне лучше купить?" - "Which dress would I better buy?" - asking for an advice rather than order. "Какое лучше купить?" - the more conversational, informal shortened phrase. Assuming the contexts is immediately available.
"Какое [платье] покупаем?" - "Which dress we are buying now?". Considers the purchase as a joint activity. The wallet is not necessarily shared, but the time and opinions they were.
The "should I buy" is somewhat demanding an order. Like a family in a ties section. The husband can get a bit annoyed "All those shades look the same color to me. I see no difference. If you, sweetheart, can tell them from one another, stop trying 1000 shades of gray, just show me which damned one tie should I bye, and I accept your taste and your judgment."
(В конце концов...) (Ну и всё-таки,..) какое (же) платье мне купить? Or even "...мне покупать?"
Here it sounds to me like "...мне надлежит купить?" - "...I ought to buy?". Or "...какое же платье ты мне скажешь купить?" - "...you would tell me to buy?"
In a casual non-stressed situation, i'd "soften" the "buy" verb by "лучше" (just want you non-binding opinion) or by plural inclination (we are together in this activity). The direct indefinite-tense "мне купить" would sound annoyed to my ear.