In RM2 core, the only human races were Common or High Men. Common Men got +5 St, and 0 to everything else, whereas High Men got +10 St, +10 Pr, +10 Con, +5 to Cha saves, as well as a higher hit die (d10 as opposed to d8) and max hits (150 vs. 120), so they were the stronger choice for humans in many cases (though they also suffered -5 Qu, -5 Ag, and -5 to Ess/Men saves).
The extra races that came out with Rolemaster Companion I changed all that, of course, since there were now many more human races, many of which were betters suited for some builds.
And then of course there were the Laan in Kulthea, who had still better stats. But there were also other races, most notably the Talath, who were even better for some builds (e.g. Paladins). The Kulthea races seemed to have really jacked stats, with some races having just incredibly good arrays, which led to some races being chosen inordinately frequently (Talath Paladins, Vorloi or Dyari Magicians, etc.). I don't remember the Laan being chosen as frequently as Talath or Vorloi though.