There are a lot of threads on this subject. Basically, IMO, having owned 12s from Yamaha, Ovation, Guild, Seagull, and Taylor and having played a lot of others, there is no such thing as a non-jangly 12 string!
FWIW, a Martin D12-28 had the least jankly sound of any 12 I have played but I ended up choosing a Taylor GS5 over it in many hours of comparing the two at a shop because the Taylor seemed to have a slightly better overall balance.
However, much can be done to address that but the approach also depends on what you will be doing with it. If you are using it to accompany yourself as a vocalist, you have to consider how the guitar will work with your voice. FOR MY USE, tuning down is not workable/useable. Sure, in theory you can capo E position chords up a few frets to keep a song in "E" (for example) rather than playing E in a tuned-down guitar and ending up in (say) C#. BUT IMO for most songs, capos rob guitars of much of their resonance so I don't like using them except in very rare instances. THe sound of a guitar playing in c position cappoed up 3 is pretty anemic compared to playing in E un-capoed.
Obviously, what keys you end up in is determined by your own vocal range plus the sound you want from the guitar.
I'm quite pleased with my Taylor GS5's sound tuned to standard pitch with the following changes: The octave e and a strings are removed, making it a 10 string. The E and A string are heavy gauge, all the rest are lights. These changes give it much better bass sound than the oem setup. The octave strings e and a actually reduce the perceived bass so just removing them will make a useful difference. Going to heavy gauge strings on E and A will increase the actual bass. Because the e and a are removed, the total tension on the bridge is no higher than a full set of light gauge strings so there is no issue with tension.
Ironically, the changes I made to the Taylor probably made it sound more like the Martin 12-28 did in the first place.
It would be interesting to re-do that comparison...