I think the guild Wayward Flock (they have a page on Argentarchives) might be something you are looking for. They’re a mixed race adventuring guild and neutral, cooperating with some similarly minded Horde guilds from my understanding.
The Wayfarer Association ([A-RP] The Wayfarer Association - Adventure with Friends) has a similar touch, I believe, but they may not be neutral.
The Crystal Path ([A RP] The Crystal Path – Year 3 (Champions of Azeroth RP)) is a bit more “organised” adventuring, I think and power levels within may be higher than the guilds I mentioned above (I’m not 100% sure, though).
Generally I would recommend scouring through argentarchives. There’s a lot of guilds on there that fit your criteria, I believe.