I wasn't sure if this was already a thread or not...looked, but didn't see anything...
Manga has a lot of publishers these days.
Most notable are:
But there are others out there too.
Sometimes I find that I have a preference for which publishers I buy.
TokyoPOP has been great, but lately their new manga doesn't have the same quality it used to.
VIZ has a lot of Shonen Jump manga, which is great, but there's not much variation.
Some up and coming companies that I thoroughly enjoy have been Go!Comi, CMX, and Yen Press.
Darkhorse (The publisher of the Trigun manga and others) have published a few, and they're pretty good.
Maybe it doesn't matter to you, but I suppose it matters to me xD
Who do you prefer?