For alsa, all you need is alsa.tcel from tha appbrowser and it will install the alsa-modules as a dependency.
As for whether alsa or OSS is better, depends on your hardware and sometimes software situation. Each has it's own good and bad points, and each has it's fans. OSS does not get locked to one application and that could save some headache at times.
OSS and alsa are best not to install at the same time unless you really know what you are doing. Their modules get autoloaded upon loading the extension.