Pretty much all the servers. I've been lending out my account to some friends who wanted to see content ahead of time on TW, and on NA I've been mainly focused on competitive SDGO since that would, and will never happen on KR for us foreigners. I've been trying to knock myself back in the mood for TW, but the general play attitude combined with our natural lag and high oc / cheap suit selection of TW players makes it hard to enjoy it for a few games. Like a friend of mine remarked when we were both playing, it's disheartening when a person in Rau can literally carry a room, yet play worse then a new NA player right when they swap to K-Ball or another suit.
The other reason why I've never been interested in playing in TW, is the staggered release schedule on top of S rank milking. While the gachas are a good deal for newer players, if you have an accrued collection, it's hard to justify the entry fee when most of the suits are recycles that you already possess but Wasabii deems as profitable. However, if NA goes down a terrible road and ruins the S rank releases, or staggers out the content releases, I'll probably give TW a harder look.
TLDR: Playing NA with a sidefocus on TW BNG, though with the current state of the 3 main servers, things are set to change at any real moment.