NeoOffice is the best "OS X-native" version of OpenOffice, for the moment. While the official OpenOffice.org release is, technically, OS X native, NeoOffice has better integration. If you really want to try the "official" OpenOffice.org release, then you want Aqua. If you don't know what X11 means, then you can't even use it. (Aqua is the OS X "windowing system", while X11 is the UNIX windowing system. X11 isn't even installed on OS X by default, but you can choose to add it and run X11-based UNIX apps. Including their usually horrendous interfaces.)
As for bloat, running OpenOffice carries with it the 'bloat' of running X11, although X11 isn't too bad. NeoOffice has a slower-to-respond interface than OpenOffice on older hardware, but anything faster than 1 GHz should be fast enough to be barely noticeable. Neither one is a memory hog, but they ARE "full featured" office suites, so they aren't LIGHT on memory usage, either.