I'm notating a 3/4 time the music is slow. I have two notes, how do I write it two dotted quarter notes (a quarter plus a eighth) or two quarter notes with a bracket with a two on top. (The same way when notating triplets, we use three in the place of two. Here it's the opposite two quarters in the place of three quarters)
There is definitely a "right" and a "wrong" way to notate something (think of stems on the wrong side of the note head, etc), but in this case, I think it's more a question of whether one way is "better" than another or more appropriate in one case over another. In a nutshell, I think the notation should support the musical interpretation.
Here's the way I look at them. Consider a short segment I composed in the last ten minutes, subject to the community's stern ridicule:
Some have suggested dotted-quarter + eighth tied to quarter. For a piece like this, such a notation seems unfitting. In my humble opinion, for a simple triple meter, that would be more fitting in a context like the following:
which, to my memory, once teacher of mine said resembled a South American rhythm. It seems to suggest, "Make sure the one hand emphasizes its rhythmic syncopation against the other." Whatever the case, I believe it has a certain mood and that the notation appropriately reflects it.
In this case, we have a notation that looks more like there's one flowing melody line. I like this in some contexts, but in this one, for such a short line, especially next to the quarter notes in the 5th measure, it might feel out of place. Even after the 9th measure, at the descending scale, there's a very slight possibility that a musician whose attention lapses for a split second may see a dotted half followed by dotted quarters, and play in duple compound meter. Maybe for a longer passage, this would be more suitable. Indeed, for an improvisation of mine that I transcribed, I decided it would be the most suitable notation:
I fully admit that this may be personal preference, but when I see that style of notation, with the tuplet bracket and the 2's, I get the sense that the author means for this to be "brought out" or emphasized, even if slightly. For a "flowing" piece like this one, I would pay more careful attention to those sections and take pains to properly convey them. In other words, it suggests, "Play one hand in 2, the other in 3, and don't make it sound syncopated, or play against the other, but let them both live and breathe in harmony." I know that sounds fruity, but it's how I approach passages sometimes.
Hopefully, this gives you some thoughts and guidance on how to use these three ways of notating the same "information."
If the tempo doesn't change, I'd do it another way: dotted quarter then eighth tied to quarter. I used to prefer two dotted quarters but my favored way now keeps a visual indication of the underlying 3/4 pulse and allows the noise to sound of half a bar. All the scores (mostly classical, big band, Latin American, ....) I have seen recently use the dotted quarter followed by the eighth-quarter tie. Most engraving books recommend keeping the notes aligned with the time signature.
Not particularly seen it, but a crotchet tied to a quaver/ quaver tied to a crotchet would do the trick - the tie there showing a push to the rhythm rather like you'd see across the middle of a 4/4 bar, where a tie keeps the physical divide in two halves, and when seen, indicates a syncopation. (Crotchet = quarter, quaver = eighth).
It is a bit of a tossup. A very handwavy rule is that you use duoles mainly when the inner rhythm does not interact with the outer rhythm. When you are talking about slow music and dotted quarters, that is rather improbable.
There have been a few suggestions of using tied notes: that is only called for when the rhythm interacts strongly with the outer rhythm, like when the bass/rhythm group syncopates a beat while the melody keeps the normal accents. For combo use, notating strongly to the beat is pretty customary.
For the case where there are just two notes to the 3/4 measure, I would in most music styles prefer just seeing dotted quarters.