This thread is just about the commands and not the actual releases, correct? If so, then yes, there is no thread like this.
I suppose my favorite command thus far is Yama-jii's. I would have to look up the actual Japanese, but when I first saw the English translation "reduce the whole of creation to ash," I have been in love with that command ever since.
My next favorite would be Shunsui's. It is like a nice little poem about flowers, wind, and gods.
If I were to pick an arrancar release command especially, it would be Nelliel's utae. "Declare" just sounds really cool to me.
I would find it a tad hard to choose any but shunsui's, ukitake's and yamamoto's release command. They are the only ones that have more than a single or a couple of words. I guess I like ukitake's shikai command with the whole wave and thunder thing it has going on.
Please remember that you need to post some sort of reasoning with your choices. Posts that contain no reasons will be subject to deletion.
"Souten ni zase HYOURINMARU"
...because I like how they sound.
Grind Pantera: Grimmjow
Dance Sode no Shirayuki: Rukia
Otherwise everyone has said my favorites; Yama, Shunsui, and Ukitake. The one word commands sound so dramatic in the anime, I like them a little less written down. The two I posted sound cool no matter what
Ive got three that I like to above the rest:
Byakuya's "chire Senbonzakura" sounds great in Japanese. I'm not a huge fan of the English translation of scatter, but when you combine the command and the animation of the blade scattering it does look pretty cool.
Mayuri's "kamushire ashisogi jizo" sounds cool both ways. The English translation "tear off" sounds even better than the Japanese translation
Ulquiorra "tozase Murcielago" is more about the animation that goes along with the actual command. It gets all dark and you kind of see how somebody is enclosed in the despair.
Starrk's "kechirase los lobos" is up there, but... the result is kind of a let down and "kick about" doesn't really inspire fear lol
My favorite releases have to be the 9th espadas 'Glotoneria' and the one from the woman Privaron espada 'golondrina'. The pronunciation is so awful it's both funny and cool. I had quit the anime for a long time so I am not aware of other releases; like Ulq's and Nnoitra's.
Shinigami's ... .... ... ... I shamefully give mine to Hitsugaya 'freeze heavens.. something.'. Yama's is a second place.