The question you've asked might not be possible to answer, and I think investigating why will help us get you an answer.
First, neither polities had a group of people they called 'commoners'. In Rome, probably the closest we have are plebs - non-noble citizens, who would have ranged from wealthy to poor (and experienced different qualities of life), and we would be talking about both urban and rural peoples. In Anglo-Saxon England (and the situation would have been different in Wales, Scotland and Ireland), society was broken between peasant churls and nobility of various ranks, from thane to alderman. Peasant life would have differed between urban and rural (the majority living in rural). And both societies had slaves in large numbers, and fifty percent of the population - the women - experienced life differently, with usually far more limitations on their freedoms than their brothers, fathers and sons.
The next issue is geographic scope and societal differences. Rome in 500 BC was a city state, one of many in Italy/the Mediterranean, and its early days are cloaked in myth (Rome only became a republic around 500 BC). The question might be easier to answer if moved forward a few centuries, into the heyday of the republic or during the empire. Rome, for much of its history, was a city state, so you're talking about people within a narrow geographic area. Britain in 1000 AD was split between England, Scotland, and smaller territories in Ireland and Wales, and the experiences of 'commoners' varied from state to state. Life was structured differently to Rome: where Rome was mainly urban, England was mainly agrarian. Where Roman life was defined by your relationship to the city (whether you were a citizen or not, what duties you owed the state and what the state owed to you), Churls had a relationship to the land and their landowners.
Life was so very different between the two places that it is difficult to compare if one was 'better' than the other, and is probably unanswerable. I can guess that most of us today would consider the urban Roman life preferable, because it is in some ways more relatable to us than medieval British life, but that doesn't mean it is 'better'. You will also struggle to find someone who knows both Roman and British history well enough to provide a meaningful answer covering both halves of the question.
But there are two really interesting questions here: what was life life in the early Roman republic, especially for non-nobles? What was life like for peasants in the British isles in 1000 AD?
If you don't get an answer here (and hopefully you do, lots of interest), perhaps you'll want to break the question in two, and you might get more luck that way.
If only there was some way to pierce the veil and see what these censorious AH mods are keeping from u--
oh no
So, by my current count, of the 68 comments in this thread excluding this post, there are 48 comments asking or complaining about removed comments, another ~10-15 asking or discussing unnecessary follow-ups under our follow-up rule, four insufficient attempts to answer OP's question which didn't meet our standards, and several further useless one-line responses. You're not missing much.
Hi folks,
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https://www.reddit.com/r/AskHistorians/comments/8p0s9b/roundtable_21_be_kindremind_the_mod_approved/