In terms of literature, the Anglo Normans probably contributed more to what we consider today as the richest and most valuable historical works. The notable exception is Beowulf, the Anglo Saxon masterpiece, an epic poem that is well known and studied even today. However, Beowulf stands out so much in part because it stands alone.

Anglo Norman literature encompasses a wide variety of topics. Probably the most enduring are the medieval Romances—stories of chivalrous knights and courtly ladies, with a famous example being Tristan and Isolde. There were also some notable biographies and histories written during Anglo Norman times, such as the tale of the lost Edward, also known as the "Black Prince."

Theater plays and poetry also figured prominently in Anglo Norman literature. Many of the plays dealt with religious themes, such as the lives of the saints. Several of these plays were written with specific religious orders in mind, in hopes of connecting the monks and nuns to the story of their patron saint. More secular works exist, too, such as the "lays," or fables, of Marie de France. These short stories, often with romantic or magical elements, are renowned and studied even today.

In short, when considering which culture contributed more to our literary history, it seems you have to choose the Anglo Normans. However, do not forget to give the Anglo Saxons their due when it comes to Beowulf.

Which era, in term of treasuring enriched literature, contributed more, Anglo Saxon or Anglo Norman?

To answer your question, we first need to establish the length of the respective periods: the Anglo-Saxon period is considered to be between 250 CE and 1066 CE, and the Anglo-Norman Period is between 1066 CE and about the middle of the fourteenth century. This is when, in 1362, Edward III replaced French with English in law courts. By 1385, English became the dominant language for schools.

We must also acknowledge that the periods overlapped to some degree in terms of the literature being written. And to respond to your question about which period treasured its literature more and contributed more to English literature, I would have to say that the cultures of both periods treasured their literature equally and both contributed to the heritage of literature in England equally, perhaps with a slight edge to the Anglo-Saxon Period.

During the Anglo-Saxon Period, for example, an anonymous monk composes the epic poem Beowulf, not only the only surviving epic poem in Old English but the only surviving epic in any Germanic language. Beowulf, which survives in only one manuscript, is a foundational work of English literature because it holds a mirror up to the culture that dominates England for almost a millennium. A shorter epic, the Finnsburg Fragment, is included in Beowulf but recounts a Scandinavian dynastic struggle separate from the Beowulf epic and, unlike Beowulf, does not contain Christian references.

Another culturally important poem is Widseth, written about 725 CE, which recounts the journey of a bard named Widseth who tells of his journey around the courts of several Anglo-Saxon kings. Other significant poems that we study in order to understand the Anglo-Saxon world view are The Seafarer, The Wanderer, Deor's Lament, Wulf and Eadwacer, and The Wife's Lament, which is about a woman separated from her husband.

In about 670, we have the advent of a flood of ecclesiastical works, beginning with the Venerable Bede's History of the English People, which recounts the history of the English people from the Roman invasion in 54 BCE to 731 CE, the best history we have of the English people until the 1600s. During the reign of Alfred the Great (ca. 849 to 900 CE), and most likely at his direction, a group of monks began compiling the Anglo-Saxon Chronicle, a year-by-year history of the Anglo-Saxon people, which extends beyond Alfred's life and is considered the most significant example of prose in Old English. The Chronicle, in its longest version, records events as late as 1153 CE, and linguists are able to study the transition from Old English to early Middle English.

Although it is commonplace to say that Anglo-Saxon literature ends with the Norman Conquest in 1066, the fact is, the culture and language persists among the common people even though the literate class—clerics and the aristocracy—speaks French and Latin, and much of the literature begins to mirror the language of its readers and listeners.

In about 1140, Geoffrey of Monmouth, a Benedictine monk who is considered the founder of the Arthurian epic produces the Historia Regum Britanniae, introducing King Arthur to the English landscape. A few years later, Robert Wace, another cleric, essentially translates Geoffrey's Historia into French, adds a few details to the Arthurian legend (the Round Table), and incorporates many of the elements of French chivalry into the story. In about 1205, Layamon (pronounced Lagamon) writes what we refer to as Layamon's Brut, essentially a verse translation of Wace, yet another work about Arthur but, perhaps most important, it is written in early Middle English and relies heavily on Old English alliterative verse and diction.

Following the flowering of Arthurian romances, we have many religious poems in early Middle English—Ancrene Riwle (Rule for Anchoresses), Ayenbite of Inwit (Remorse of Conscience)—and several secular poems like The Owl and the Nightingale (ca. 1255), a debate about whether a religious life or worldly life is better. After the mid-1200s, the French language is declining steadily even among the aristocracy, and the literature that remains is increasingly rendered in Middle English.

The Anglo-Norman Period, although it lasts from 1066 to about 1350, ends almost in a whimper, and its literature, though certainly a vital part of English literary history—where would we be without Arthur and the Round Table?—is absorbed by a language, English, that is so central to most of the population that French-centered literature, no longer representative of even the aristocracy, cannot survive.

Which era, in term of treasuring enriched literature, contributed more: Anglo-Saxon or Anglo-Norman?

Both periods of English history have produced pieces of literature we treasure, but in terms of English literature, more treasured pieces have come down to us from the Anglo-Norman period. This is not to say that the Anglo-Saxons didn't value or produce great literature, but less of it has survived.

The main work in the English literary tradition that is treasured from Anglo-Saxon literature is Beowulf. It's difficult to overestimate the value of this work. It has provided an archetype of the knight-hero slaying the monster/dragon that became a common motif in Anglo-Norman literature, used alliteration in ways that were imitated by the Anglo-Normans (not to mention modern writers), and provided a template that has in many ways, through writers like Tolkien, become immensely popular in twentieth and twenty-first century fantasy literature.

A greater volume of treasured literature, however, survives from the Anglo-Norman period. At that point, the Normans had invaded and conquered England, and the Germanic English language became heavily inflected with French and romance language elements. The shift in language was so dramatic that it became called Middle English. This is the first language that is close enough to modern English, at least in its London dialect, that we can read as recognizable, if alien, English.

This later Medieval period produced a great flourishing of literature, and we remember such towering figures as Chaucer and the Gawain poet, and the growth of such genres as rood poetry, allegorical religious drama, and Arthurian romance. So many genres developed and flourished during this period, from bawdy humor to deeply-felt emotional poetry that the Renaissance—and the modern era—has had much to borrow from.