Do you find good translations equal in both tongues, or is there always a transmission loss. Or have you even encountered a translation executed with such skill as to be an improvement on the original?
As someone who has translated poetry (Danish to English professionally, German to English but not published or paid), while there are definitely "bad" translations that do damage to a poem, I don't think it's right to say there is always a "loss" in translation. There are always differences between the original and the translation but, with a good and careful translation, those differences can be enriching in multiple ways. Changes in rhythm and rhyme might alter the tone, even speed, of a poem and subtly change its reception. Changes in words with no precise cognate in the target language may shift meaning in small, even large, ways. Idiom, in particular, is a minefield and often requires significant changes to arrive at a similar point and the use of names or references to cultural touchstones (for example, Biblical references in much of Western literature) raise tricky problems.
Personally, some of my favourites are Michael Hamburger's translations of Paul Celan, Coleman Barks' translations of Rumi and FitzGerald's translation of Omar Khayyam's
Rubaiyat. FitzGerald took huge liberties with the
Rubaiyat, essentially changing its structure and writing new couplets based on Khayyam, rather than truly translating him. That is, almost by definition, a bad translation, and yet, almost 200 years later, the imagery and rhythm of his version is, for me, still more powerful than any other English translation I've read. Coleman Barks took liberties, as well, but generally stayed quite true to Rumi while communicating the wit, humour and profound love of the poetry. Of these three, Hamburger stays closest to the original and, since I can read Celan in German, I can examine the differences between the two versions, question the spots where Hamburger deviated from the original and admire the subtlety of his thinking as revealed by his choices.
All of that said, while I find some translations to be as interesting, compelling or as moving as the originals, I can't think of any where I found the translation to be better.