Hey, I wrote an answer here about the oft-confusing use of terminology in "feudal" sources that may prove interesting. It's worth noting that "freeholder" and "peasant" are far from mutually exclusive terms, while "serf" is itself a very mutable term that is not always actually useful, or reflected in contemporary sources. Assuming that you intend for "serf" to mean tenant farmers, in early medieval sources such as Domesday Book, these are villanus, villagers, cottagers, smallholders, boarders, borderers or other ranks of the complex social hierarchy of the agrarian peasantry. The servus of Domesday are literal slaves, mostly but far from entirely Welsh, who comprise about 10% of listed households. It's likely slavery had been declining for some decades at this point, so the earlier figure is likely to be much higher, and it appears to have mostly disappeared by the 1120s.

Freeholders are more often than not listed as "Freemen", which provides the added fun of then distinguishing them from the "free men" who comprise the rest of the peasantry who are not of slave class. It's worth pointing out that these individuals would themselves have been peasantry, unless they had owned more 5 'hides' of land which would have qualified them as thegns. At Domesday, around 10-14% of households are freeholders. It's likely that this number is a decrease from prior to 1066, and one that would decrease again somewhat in some areas in the twelfth century. A higher concentration of freeholders is found in the North and East, although there is debate as to whether this may be because West Saxon peasants largely lost freeman status during bureaucratic reforms in response to the Anglo-Danish wars in the 9th Century, whether there was simply a higher proportion of freeholding in East Anglia, or whether Danish settlers, by dint of conquest, were simply able to establish themselves as freeholders more successfully in these areas. A similar phenomenon occurs in the twelfth century along the Anglo-Welsh marches, as Marcher Lords looking to secure new territory in Wales often recruit large warbands from among their peasantry who would hope to secure freeholder rights, or at least better status, in newly conquered lands.